MEDIUM severity: Use of two-step ownable. If ownership transfer is not done appropriately, the current contract owner can renounce/transfer ownership, lose owner privileges, and lose the ability to burn tokens.

Vulnerable code:
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

interface IERC20 {
    /**
     * @dev Returns the amount of tokens in existence.
     */
    function totalSupply() external view returns (uint256);

    /**
     * @dev Returns the amount of tokens owned by `account`.
     */
    function balanceOf(address account) external view returns (uint256);

    /**
     * @dev Moves `amount` tokens from the caller's account to `recipient`.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transfer(address recipient, uint256 amount) external returns (bool);

    /**
     * @dev Returns the remaining number of tokens that `spender` will be
     * allowed to spend on behalf of `owner` through {transferFrom}. This is
     * zero by default.
     *
     * This value changes when {approve} or {transferFrom} are called.
     */
    function allowance(address owner, address spender) external view returns (uint256);

    /**
     * @dev Sets `amount` as the allowance of `spender` over the caller's tokens.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * IMPORTANT: Beware that changing an allowance with this method brings the risk
     * that someone may use both the old and the new allowance by unfortunate
     * transaction ordering. One possible solution to mitigate this race
     * condition is to first reduce the spender's allowance to 0 and set the
     * desired value afterwards:
     * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
     *
     * Emits an {Approval} event.
     */
    function approve(address spender, uint256 amount) external returns (bool);

    /**
     * @dev Moves `amount` tokens from `sender` to `recipient` using the
     * allowance mechanism. `amount` is then deducted from the caller's
     * allowance.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transferFrom(
        address sender,
        address recipient,
        uint256 amount
    ) external returns (bool);

    /**
     * @dev Emitted when `value` tokens are moved from one account (`from`) to
     * another (`to`).
     *
     * Note that `value` may be zero.
     */
    event Transfer(address indexed from, address indexed to, uint256 value);

    /**
     * @dev Emitted when the allowance of a `spender` for an `owner` is set by
     * a call to {approve}. `value` is the new allowance.
     */
    event Approval(address indexed owner, address indexed spender, uint256 value);
}
/**
 * @dev Interface for the optional metadata functions from the ERC20 standard.
 *
 * _Available since v4.1._
 */
interface IERC20Metadata is IERC20 {
    /**
     * @dev Returns the name of the token.
     */
    function name() external view returns (string memory);

    /**
     * @dev Returns the symbol of the token.
     */
    function symbol() external view returns (string memory);

    /**
     * @dev Returns the decimals places of the token.
     */
    function decimals() external view returns (uint8);
}
/*
 * @dev Provides information about the current execution context, including the
 * sender of the transaction and its data. While these are generally available
 * via msg.sender and msg.data, they should not be accessed in such a direct
 * manner, since when dealing with meta-transactions the account sending and
 * paying for execution may not be the actual sender (as far as an application
 * is concerned).
 *
 * This contract is only required for intermediate, library-like contracts.
 */
abstract contract Context {
    function _msgSender() internal view virtual returns (address) {
        return msg.sender;
    }

    function _msgData() internal view virtual returns (bytes calldata) {
        this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
        return msg.data;
    }
}

contract Ownable is Context {
    address private _owner;

    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

    /**
     * @dev Initializes the contract setting the deployer as the initial owner.
     */
    constructor () {
        address msgSender = _msgSender();
        _owner = msgSender;
        emit OwnershipTransferred(address(0), msgSender);
    }

    /**
     * @dev Returns the address of the current owner.
     */
    function owner() public view returns (address) {
        return _owner;
    }

    /**
     * @dev Throws if called by any account other than the owner.
     */
    modifier onlyOwner() {
        require(_owner == _msgSender(), "Ownable: caller is not the owner");
        _;
    }

    /**
     * @dev Leaves the contract without owner. It will not be possible to call
     * `onlyOwner` functions anymore. Can only be called by the current owner.
     *
     * NOTE: Renouncing ownership will leave the contract without an owner,
     * thereby removing any functionality that is only available to the owner.
     */
    function renounceOwnership() public virtual onlyOwner {
        emit OwnershipTransferred(_owner, address(0));
        _owner = address(0);
    }

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     * Can only be called by the current owner.
     */
    function transferOwnership(address newOwner) public virtual onlyOwner {
        require(newOwner != address(0), "Ownable: new owner is the zero address");
        emit OwnershipTransferred(_owner, newOwner);
        _owner = newOwner;
    }
}

/**
 * @dev Implementation of the {IERC20} interface.
 *
 * This implementation is agnostic to the way tokens are created. This means
 * that a supply mechanism has to be added in a derived contract using {_mint}.
 * For a generic mechanism see {ERC20PresetMinterPauser}.
 *
 * TIP: For a detailed writeup see our guide
 * https://forum.zeppelin.solutions/t/how-to-implement-erc20-supply-mechanisms/226[How
 * to implement supply mechanisms].
 *
 * We have followed general OpenZeppelin guidelines: functions revert instead
 * of returning `false` on failure. This behavior is nonetheless conventional
 * and does not conflict with the expectations of ERC20 applications.
 *
 * Additionally, an {Approval} event is emitted on calls to {transferFrom}.
 * This allows applications to reconstruct the allowance for all accounts just
 * by listening to said events. Other implementations of the EIP may not emit
 * these events, as it isn't required by the specification.
 *
 * Finally, the non-standard {decreaseAllowance} and {increaseAllowance}
 * functions have been added to mitigate the well-known issues around setting
 * allowances. See {IERC20-approve}.
 */
contract ERC20 is Context, IERC20, IERC20Metadata {
    using SafeMath for uint256;

    mapping(address => uint256) private _balances;

    mapping(address => mapping(address => uint256)) private _allowances;

    uint256 private _totalSupply;

    string private _name;
    string private _symbol;

    /**
     * @dev Sets the values for {name} and {symbol}.
     *
     * The default value of {decimals} is 18. To select a different value for
     * {decimals} you should overload it.
     *
     * All two of these values are immutable: they can only be set once during
     * construction.
     */
    constructor(string memory name_, string memory symbol_)  {
        _name = name_;
        _symbol = symbol_;
    }

    /**
     * @dev Returns the name of the token.
     */
    function name() public view virtual override returns (string memory) {
        return _name;
    }

    /**
     * @dev Returns the symbol of the token, usually a shorter version of the
     * name.
     */
    function symbol() public view virtual override returns (string memory) {
        return _symbol;
    }

    /**
     * @dev Returns the number of decimals used to get its user representation.
     * For example, if `decimals` equals `2`, a balance of `505` tokens should
     * be displayed to a user as `5,05` (`505 / 10 ** 2`).
     *
     * Tokens usually opt for a value of 18, imitating the relationship between
     * Ether and Wei. This is the value {ERC20} uses, unless this function is
     * overridden;
     *
     * NOTE: This information is only used for _display_ purposes: it in
     * no way affects any of the arithmetic of the contract, including
     * {IERC20-balanceOf} and {IERC20-transfer}.
     */
    function decimals() public view virtual override returns (uint8) {
        return 18;
    }

    /**
     * @dev See {IERC20-totalSupply}.
     */
    function totalSupply() public view virtual override returns (uint256) {
        return _totalSupply;
    }

    /**
     * @dev See {IERC20-balanceOf}.
     */
    function balanceOf(address account) public view virtual override returns (uint256) {
        return _balances[account];
    }

    /**
     * @dev See {IERC20-transfer}.
     *
     * Requirements:
     *
     * - `recipient` cannot be the zero address.
     * - the caller must have a balance of at least `amount`.
     */
    function transfer(address recipient, uint256 amount) public virtual override returns (bool) {
        _transfer(_msgSender(), recipient, amount);
        return true;
    }

    /**
     * @dev See {IERC20-allowance}.
     */
    function allowance(address owner, address spender) public view virtual override returns (uint256) {
        return _allowances[owner][spender];
    }

    /**
     * @dev See {IERC20-approve}.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function approve(address spender, uint256 amount) public virtual override returns (bool) {
        _approve(_msgSender(), spender, amount);
        return true;
    }

    /**
     * @dev See {IERC20-transferFrom}.
     *
     * Emits an {Approval} event indicating the updated allowance. This is not
     * required by the EIP. See the note at the beginning of {ERC20}.
     *
     * Requirements:
     *
     * - `sender` and `recipient` cannot be the zero address.
     * - `sender` must have a balance of at least `amount`.
     * - the caller must have allowance for ``sender``'s tokens of at least
     * `amount`.
     */
    function transferFrom(
        address sender,
        address recipient,
        uint256 amount
    ) public virtual override returns (bool) {
        _transfer(sender, recipient, amount);
        _approve(sender, _msgSender(), _allowances[sender][_msgSender()].sub(amount, "ERC20: transfer amount exceeds allowance"));
        return true;
    }

    /**
     * @dev Atomically increases the allowance granted to `spender` by the caller.
     *
     * This is an alternative to {approve} that can be used as a mitigation for
     * problems described in {IERC20-approve}.
     *
     * Emits an {Approval} event indicating the updated allowance.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function increaseAllowance(address spender, uint256 addedValue) public virtual returns (bool) {
        _approve(_msgSender(), spender, _allowances[_msgSender()][spender].add(addedValue));
        return true;
    }

    /**
     * @dev Atomically decreases the allowance granted to `spender` by the caller.
     *
     * This is an alternative to {approve} that can be used as a mitigation for
     * problems described in {IERC20-approve}.
     *
     * Emits an {Approval} event indicating the updated allowance.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     * - `spender` must have allowance for the caller of at least
     * `subtractedValue`.
     */
    function decreaseAllowance(address spender, uint256 subtractedValue) public virtual returns (bool) {
        _approve(_msgSender(), spender, _allowances[_msgSender()][spender].sub(subtractedValue, "ERC20: decreased allowance below zero"));
        return true;
    }

    /**
     * @dev Moves tokens `amount` from `sender` to `recipient`.
     *
     * This is internal function is equivalent to {transfer}, and can be used to
     * e.g. implement automatic token fees, slashing mechanisms, etc.
     *
     * Emits a {Transfer} event.
     *
     * Requirements:
     *
     * - `sender` cannot be the zero address.
     * - `recipient` cannot be the zero address.
     * - `sender` must have a balance of at least `amount`.
     */
    function _transfer(
        address sender,
        address recipient,
        uint256 amount
    ) internal virtual {
        require(sender != address(0), "ERC20: transfer from the zero address");
        require(recipient != address(0), "ERC20: transfer to the zero address");

        _beforeTokenTransfer(sender, recipient, amount);

        _balances[sender] = _balances[sender].sub(amount, "ERC20: transfer amount exceeds balance");
        _balances[recipient] = _balances[recipient].add(amount);
        emit Transfer(sender, recipient, amount);
    }

    /** @dev Creates `amount` tokens and assigns them to `account`, increasing
     * the total supply.
     *
     * Emits a {Transfer} event with `from` set to the zero address.
     *
     * Requirements:
     *
     * - `account` cannot be the zero address.
     */
    function _mint(address account, uint256 amount) internal virtual {
        require(account != address(0), "ERC20: mint to the zero address");

        _beforeTokenTransfer(address(0), account, amount);

        _totalSupply = _totalSupply.add(amount);
        _balances[account] = _balances[account].add(amount);
        emit Transfer(address(0), account, amount);
    }

    /**
     * @dev Destroys `amount` tokens from `account`, reducing the
     * total supply.
     *
     * Emits a {Transfer} event with `to` set to the zero address.
     *
     * Requirements:
     *
     * - `account` cannot be the zero address.
     * - `account` must have at least `amount` tokens.
     */
    function _burn(address account, uint256 amount) internal virtual {
        require(account != address(0), "ERC20: burn from the zero address");

        _beforeTokenTransfer(account, address(0), amount);

        _balances[account] = _balances[account].sub(amount, "ERC20: burn amount exceeds balance");
        _totalSupply = _totalSupply.sub(amount);
        emit Transfer(account, address(0), amount);
    }

    /**
     * @dev Sets `amount` as the allowance of `spender` over the `owner` s tokens.
     *
     * This internal function is equivalent to `approve`, and can be used to
     * e.g. set automatic allowances for certain subsystems, etc.
     *
     * Emits an {Approval} event.
     *
     * Requirements:
     *
     * - `owner` cannot be the zero address.
     * - `spender` cannot be the zero address.
     */
    function _approve(
        address owner,
        address spender,
        uint256 amount
    ) internal virtual {
        require(owner != address(0), "ERC20: approve from the zero address");
        require(spender != address(0), "ERC20: approve to the zero address");

        _allowances[owner][spender] = amount;
        emit Approval(owner, spender, amount);
    }

    /**
     * @dev Hook that is called before any transfer of tokens. This includes
     * minting and burning.
     *
     * Calling conditions:
     *
     * - when `from` and `to` are both non-zero, `amount` of ``from``'s tokens
     * will be to transferred to `to`.
     * - when `from` is zero, `amount` tokens will be minted for `to`.
     * - when `to` is zero, `amount` of ``from``'s tokens will be burned.
     * - `from` and `to` are never both zero.
     *
     * To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
     */
    function _beforeTokenTransfer(
        address from,
        address to,
        uint256 amount
    ) internal virtual {}
}

library Address {
    /**
     * @dev Returns true if `account` is a contract.
     *
     * [IMPORTANT]
     * ====
     * It is unsafe to assume that an address for which this function returns
     * false is an externally-owned account (EOA) and not a contract.
     *
     * Among others, `isContract` will return false for the following
     * types of addresses:
     *
     *  - an externally-owned account
     *  - a contract in construction
     *  - an address where a contract will be created
     *  - an address where a contract lived, but was destroyed
     *
     * Furthermore, `isContract` will also return true if the target contract within
     * the same transaction is already scheduled for destruction by `SELFDESTRUCT`,
     * which only has an effect at the end of a transaction.
     * ====
     *
     * [IMPORTANT]
     * ====
     * You shouldn't rely on `isContract` to protect against flash loan attacks!
     *
     * Preventing calls from contracts is highly discouraged. It breaks composability, breaks support for smart wallets
     * like Gnosis Safe, and does not provide security since it can be circumvented by calling from a contract
     * constructor.
     * ====
     */
    function isContract(address account) internal view returns (bool) {
        // This method relies on extcodesize/address.code.length, which returns 0
        // for contracts in construction, since the code is only stored at the end
        // of the constructor execution.

        return account.code.length > 0;
    }

    /**
     * @dev Replacement for Solidity's `transfer`: sends `amount` wei to
     * `recipient`, forwarding all available gas and reverting on errors.
     *
     * https://eips.ethereum.org/EIPS/eip-1884[EIP1884] increases the gas cost
     * of certain opcodes, possibly making contracts go over the 2300 gas limit
     * imposed by `transfer`, making them unable to receive funds via
     * `transfer`. {sendValue} removes this limitation.
     *
     * https://consensys.net/diligence/blog/2019/09/stop-using-soliditys-transfer-now/[Learn more].
     *
     * IMPORTANT: because control is transferred to `recipient`, care must be
     * taken to not create reentrancy vulnerabilities. Consider using
     * {ReentrancyGuard} or the
     * https://solidity.readthedocs.io/en/v0.5.11/security-considerations.html#use-the-checks-effects-interactions-pattern[checks-effects-interactions pattern].
     */
    function sendValue(address payable recipient, uint256 amount) internal {
        require(address(this).balance >= amount, "Address: insufficient balance");

        (bool success, ) = recipient.call{value: amount}("");
        require(success, "Address: unable to send value, recipient may have reverted");
    }

    /**
     * @dev Performs a Solidity function call using a low level `call`. A
     * plain `call` is an unsafe replacement for a function call: use this
     * function instead.
     *
     * If `target` reverts with a revert reason, it is bubbled up by this
     * function (like regular Solidity function calls).
     *
     * Returns the raw returned data. To convert to the expected return value,
     * use https://solidity.readthedocs.io/en/latest/units-and-global-variables.html?highlight=abi.decode#abi-encoding-and-decoding-functions[`abi.decode`].
     *
     * Requirements:
     *
     * - `target` must be a contract.
     * - calling `target` with `data` must not revert.
     *
     * _Available since v3.1._
     */
    function functionCall(address target, bytes memory data) internal returns (bytes memory) {
        return functionCallWithValue(target, data, 0, "Address: low-level call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`], but with
     * `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCall(
        address target,
        bytes memory data,
        string memory errorMessage
    ) internal returns (bytes memory) {
        return functionCallWithValue(target, data, 0, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but also transferring `value` wei to `target`.
     *
     * Requirements:
     *
     * - the calling contract must have an ETH balance of at least `value`.
     * - the called Solidity function must be `payable`.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(address target, bytes memory data, uint256 value) internal returns (bytes memory) {
        return functionCallWithValue(target, data, value, "Address: low-level call with value failed");
    }

    /**
     * @dev Same as {xref-Address-functionCallWithValue-address-bytes-uint256-}[`functionCallWithValue`], but
     * with `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(
        address target,
        bytes memory data,
        uint256 value,
        string memory errorMessage
    ) internal returns (bytes memory) {
        require(address(this).balance >= value, "Address: insufficient balance for call");
        (bool success, bytes memory returndata) = target.call{value: value}(data);
        return verifyCallResultFromTarget(target, success, returndata, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but performing a static call.
     *
     * _Available since v3.3._
     */
    function functionStaticCall(address target, bytes memory data) internal view returns (bytes memory) {
        return functionStaticCall(target, data, "Address: low-level static call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-string-}[`functionCall`],
     * but performing a static call.
     *
     * _Available since v3.3._
     */
    function functionStaticCall(
        address target,
        bytes memory data,
        string memory errorMessage
    ) internal view returns (bytes memory) {
        (bool success, bytes memory returndata) = target.staticcall(data);
        return verifyCallResultFromTarget(target, success, returndata, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but performing a delegate call.
     *
     * _Available since v3.4._
     */
    function functionDelegateCall(address target, bytes memory data) internal returns (bytes memory) {
        return functionDelegateCall(target, data, "Address: low-level delegate call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-string-}[`functionCall`],
     * but performing a delegate call.
     *
     * _Available since v3.4._
     */
    function functionDelegateCall(
        address target,
        bytes memory data,
        string memory errorMessage
    ) internal returns (bytes memory) {
        (bool success, bytes memory returndata) = target.delegatecall(data);
        return verifyCallResultFromTarget(target, success, returndata, errorMessage);
    }

    /**
     * @dev Tool to verify that a low level call to smart-contract was successful, and revert (either by bubbling
     * the revert reason or using the provided one) in case of unsuccessful call or if target was not a contract.
     *
     * _Available since v4.8._
     */
    function verifyCallResultFromTarget(
        address target,
        bool success,
        bytes memory returndata,
        string memory errorMessage
    ) internal view returns (bytes memory) {
        if (success) {
            if (returndata.length == 0) {
                // only check isContract if the call was successful and the return data is empty
                // otherwise we already know that it was a contract
                require(isContract(target), "Address: call to non-contract");
            }
            return returndata;
        } else {
            _revert(returndata, errorMessage);
        }
    }

    /**
     * @dev Tool to verify that a low level call was successful, and revert if it wasn't, either by bubbling the
     * revert reason or using the provided one.
     *
     * _Available since v4.3._
     */
    function verifyCallResult(
        bool success,
        bytes memory returndata,
        string memory errorMessage
    ) internal pure returns (bytes memory) {
        if (success) {
            return returndata;
        } else {
            _revert(returndata, errorMessage);
        }
    }

    function _revert(bytes memory returndata, string memory errorMessage) private pure {
        // Look for revert reason and bubble it up if present
        if (returndata.length > 0) {
            // The easiest way to bubble the revert reason is using memory via assembly
            /// @solidity memory-safe-assembly
            assembly {
                let returndata_size := mload(returndata)
                revert(add(32, returndata), returndata_size)
            }
        } else {
            revert(errorMessage);
        }
    }
}

library SafeERC20 {
    using Address for address;

    function safeTransfer(IERC20 token, address to, uint256 value) internal {
        _callOptionalReturn(token, abi.encodeWithSelector(token.transfer.selector, to, value));
    }

    function safeTransferFrom(IERC20 token, address from, address to, uint256 value) internal {
        _callOptionalReturn(token, abi.encodeWithSelector(token.transferFrom.selector, from, to, value));
    }

    /**
     * @dev Deprecated. This function has issues similar to the ones found in
     * {IERC20-approve}, and its usage is discouraged.
     *
     * Whenever possible, use {safeIncreaseAllowance} and
     * {safeDecreaseAllowance} instead.
     */
    function safeApprove(IERC20 token, address spender, uint256 value) internal {
        // safeApprove should only be called when setting an initial allowance,
        // or when resetting it to zero. To increase and decrease it, use
        // 'safeIncreaseAllowance' and 'safeDecreaseAllowance'
        require(
            (value == 0) || (token.allowance(address(this), spender) == 0),
            "SafeERC20: approve from non-zero to non-zero allowance"
        );
        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, value));
    }

    /**
     * @dev Imitates a Solidity high-level call (i.e. a regular function call to a contract), relaxing the requirement
     * on the return value: the return value is optional (but if data is returned, it must not be false).
     * @param token The token targeted by the call.
     * @param data The call data (encoded using abi.encode or one of its variants).
     */
    function _callOptionalReturn(IERC20 token, bytes memory data) private {
        // We need to perform a low level call here, to bypass Solidity's return data size checking mechanism, since
        // we're implementing it ourselves. We use {Address-functionCall} to perform this call, which verifies that
        // the target address contains contract code and also asserts for success in the low-level call.

        bytes memory returndata = address(token).functionCall(data, "SafeERC20: low-level call failed");
        if (returndata.length > 0) {
            // Return data is optional
            require(abi.decode(returndata, (bool)), "SafeERC20: ERC20 operation did not succeed");
        }
    }
}

contract TokenReceiver {
    using SafeERC20 for IERC20;
    constructor(address token) {
        IERC20(token).safeApprove(msg.sender, type(uint).max);
    }
}

contract YYDS is ERC20, Ownable {
    using SafeERC20 for IERC20;
    IUniswapV2Router02 public uniswapV2Router;
    address public uniswapV2Pair;
    TokenReceiver public tokenReceiver;
    bool private swapping;
    bool public limitedTrade = true;

    address public constant ROUTER = 0x10ED43C718714eb63d5aA57B78B54704E256024E;
    address public constant USDT = 0x55d398326f99059fF775485246999027B3197955;
    address public marketingAddr;
    address public treasureAddr;
    address public shareholderAddr;
    address public tokenOwner;
    address public VAULT;
    address[] public nodes;

    uint256 public numTokenValueSellToSwap = 3000 * 1e18;
    uint256 public maxTokenVaulePerTx = 100 * 1e18;
    uint256 public maxTokenVauleSellPerTx = 100 * 1e18;
    uint256 public minAmountDeflation = 2000 * 1e18;
    uint256 public minAmountBurn = 2000 * 1e18;
    uint256 public intervalDays = 7;
    uint256 public buyInterval = 40 seconds;

    uint256 public buyMarketingFee = 1; 
    uint256 public sellMarketingFee = 2;
    uint256 public startTime;
    uint256 public lastDeflationTime;

    // exlcude from fees and max transaction amount
    mapping (address => bool) public isExcludedFromFees;
    mapping (address => bool) public isPair;
    mapping (address => bool) public isBlclist;
    mapping (address => uint256) public lastTimeTx;

    mapping (address => bool) public isWhitelist;
    mapping (address => uint256) public lastUpdateTime;

    uint256 public deflationFactor0 = 20;  // 2%
    uint256 public deflationFactor1 = 10; // 1%
    uint256[4] public feeShares;

    uint256 public constant SECONDS_PER_DAY = 86400;
    uint256 public constant WAD = 1e18;
    uint256 public Rate = WAD * 3 / 1000;

    modifier lockTheSwap {
        swapping = true;
        _;
        swapping = false;
    }

    constructor(
        address _marketingAddr,
        address _treasureAddr,
        address _shareholderAddr,
        address _tokenOwner
    ) ERC20("YYDS", "YYDS") {
        marketingAddr = _marketingAddr;
        treasureAddr = _treasureAddr;
        shareholderAddr = _shareholderAddr;
        tokenOwner = _tokenOwner;
        
        IUniswapV2Router02 _uniswapV2Router = IUniswapV2Router02(ROUTER);
         // Create a uniswap pair for this new token
        address _uniswapV2Pair = IUniswapV2Factory(_uniswapV2Router.factory())
            .createPair(address(this), USDT);

        uniswapV2Router = _uniswapV2Router;
        uniswapV2Pair = _uniswapV2Pair;
        isPair[_uniswapV2Pair] = true;

        tokenReceiver = new TokenReceiver(USDT);

        // exclude from paying fees or having max transaction amount
        isExcludedFromFees[owner()] = true;
        isExcludedFromFees[marketingAddr] = true;
        isExcludedFromFees[tokenOwner] = true;
        isExcludedFromFees[address(this)] = true;

        isWhitelist[owner()] = true;
        isWhitelist[address(this)] = true;
        isWhitelist[_uniswapV2Pair] = true;
        isWhitelist[address(0)] = true;
        isWhitelist[address(0xdead)] = true;

        _approve(address(this), address(uniswapV2Router), type(uint).max);

        feeShares[0] = 50;
        feeShares[1] = 15;
        feeShares[2] = 15;
        feeShares[3] = 20;
        /*
            _mint is an internal function in ERC20.sol that is only called here,
            and CANNOT be called ever again
        */
        _mint(_tokenOwner, 1000000 * 1e18);
    }

    function enableTrade() external onlyOwner {
        startTime = block.timestamp;
        lastDeflationTime = startTime;
    }

    function setDeflationFactor(uint _deflationFactor0, uint _deflationFactor1) external onlyOwner {
        require(_deflationFactor0 < 1000 && _deflationFactor1 < 1000, "invalid factor");
        deflationFactor0 = _deflationFactor0;
        deflationFactor1 = _deflationFactor1;
    }

    function setFeeShares(uint[4] memory _feeShares) external onlyOwner {
        uint totalShare = _feeShares[0] + _feeShares[1] + _feeShares[2] + _feeShares[3];
        require(totalShare == 100, "invalide feeShares");
        feeShares = _feeShares;
    }

    function setRate(uint _Rate) external onlyOwner {
        Rate = _Rate;
    }

    function setVault(address _vault) external onlyOwner {
        VAULT = _vault;
    }

    function setLimitedTrade(bool _limitedTrade) external onlyOwner {
        limitedTrade = _limitedTrade;
    }

    function setBuyInterval(uint _buyInterval) external onlyOwner {
        buyInterval = _buyInterval;
    }

    function setPair(address pair, bool value) external onlyOwner {
        isPair[pair] = value;
    }

    function excludeFromFees(address account, bool excluded) public onlyOwner {
        isExcludedFromFees[account] = excluded;
    }

    function excludeMultipleAccountsFromFees(address[] calldata accounts, bool excluded) public onlyOwner {
        for(uint256 i = 0; i < accounts.length; i++) {
            isExcludedFromFees[accounts[i]] = excluded;
        }
    }

    function setMaxTokenVaulePerTx(uint _maxTokenVaulePerTx) external onlyOwner {
        maxTokenVaulePerTx = _maxTokenVaulePerTx;
    }

    function setMaxTokenVauleSellPerTx(uint _maxTokenVauleSellPerTx) external onlyOwner {
        maxTokenVauleSellPerTx = _maxTokenVauleSellPerTx;
    }
    
    function setIntervalDays(uint _intervalDays) external onlyOwner {
        intervalDays = _intervalDays;
    }

    function setNodes(address[] memory _nodes) external onlyOwner {
        nodes = _nodes;
    }

    function setBlcList(address account, bool flag) external onlyOwner {
        isBlclist[account] = flag;
    }

    function setWhitelist(address account, bool flag) external onlyOwner {
        isWhitelist[account] = flag;
    }

    function setMultipleBlcList(address[] calldata accounts, bool excluded) external onlyOwner {
        for(uint256 i = 0; i < accounts.length; i++) {
            isBlclist[accounts[i]] = excluded;
        }
    }

    function setBuyMarketingFee(uint256 _buyMarketingFee) external onlyOwner {
        require(_buyMarketingFee < 100, "wrong parameter");
        buyMarketingFee = _buyMarketingFee;
    }

    function setMarketingWallet(address _marketingAddr) external onlyOwner {
        marketingAddr = _marketingAddr;
    }

    function setShareholderAddr(address _shareholderAddr) external onlyOwner {
        shareholderAddr = _shareholderAddr;
    }

    function setTreasureAddr(address _treasureAddr) external onlyOwner {
        treasureAddr = _treasureAddr;
    }

    function setSellMarketingFee(uint256 _sellMarketingFee) external onlyOwner {
        require(_sellMarketingFee < 100, "wrong parameter");
        sellMarketingFee = _sellMarketingFee;
    }

    function setNumTokensSellToSwap(uint256 value) external onlyOwner {
        numTokenValueSellToSwap = value;
    }

    function setMinAmountDeflation(uint256 _minAmountDeflation) external onlyOwner {
        minAmountDeflation = _minAmountDeflation;
    }

    function setMinAmountBurn(uint256 _minAmountBurn) external onlyOwner {
        minAmountBurn = _minAmountBurn;
    }

    function balanceOf(address account) public view virtual override returns (uint256) {
        uint amountPre = super.balanceOf(account);
        if (amountPre == 0) return 0;
        if (isWhitelist[account]) {
            return amountPre;
        } else {
            uint _lastUpdateTime = lastUpdateTime[account];
            uint compRate = calculateCompoundedRate(Rate, _lastUpdateTime, block.timestamp);
            return amountPre * compRate / WAD;
        }    
    }

    function calculateCompoundedRate(
        uint256 rate,
        uint256 lastUpdateTimestamp,
        uint256 currentTimestamp
    ) public pure returns (uint256) {
        uint256 exp = currentTimestamp - lastUpdateTimestamp;

        if (exp == 0) {
            return WAD;
        }

        if (exp > 365 * SECONDS_PER_DAY) {
            return WAD / 2;
        }

        uint256 expMinusOne;
        uint256 expMinusTwo;
        uint256 basePowerTwo;
        uint256 basePowerThree;
        unchecked {
            expMinusOne = exp - 1;

            expMinusTwo = exp > 2 ? exp - 2 : 0;

            basePowerTwo = rate * rate / (SECONDS_PER_DAY * SECONDS_PER_DAY) / WAD;
            basePowerThree = basePowerTwo * rate / SECONDS_PER_DAY / WAD;
        }

        uint256 secondTerm = exp * expMinusOne * basePowerTwo;
        unchecked {
            secondTerm /= 2;
        }
        uint256 thirdTerm = exp * expMinusOne * expMinusTwo * basePowerThree;
        unchecked {
            thirdTerm /= 6;
        }

        return WAD + secondTerm - (rate * exp) / SECONDS_PER_DAY  - thirdTerm;
    }

    function updateBalanceOf(address account) public {
        uint _balPre = super.balanceOf(account);
        uint _bal = balanceOf(account);
        uint diff = _balPre - _bal;
        if (diff > 0) {
            super._transfer(account, address(0xdead), diff);   
        }
        lastUpdateTime[account] = block.timestamp;
    }

    function _transfer(
        address from,
        address to,
        uint256 amount
    ) internal override {
        require(from != address(0), "ERC20: transfer from the zero address");
        require(!isBlclist[from], "blclist");
        
        if (amount == 0) {
            super._transfer(from, to, 0);
            return;
        }

        if (!isWhitelist[from]) updateBalanceOf(from);
        if (!isWhitelist[to]) updateBalanceOf(to);

        if (!isPair[from]) {
            uint maxAmount = balanceOf(from) * 99 / 100;
            if (amount > maxAmount) {
                amount = maxAmount;
            }
            deflation();
        }
            
        uint price = tokenPrice();
        uint swapToken;
        if (price == 0) {
            swapToken = numTokenValueSellToSwap;
        } else {
            swapToken = numTokenValueSellToSwap * 1e18 / price;
        }
        uint256 contractToken = balanceOf(address(this));
        bool overMinToken = contractToken >= swapToken;
        if( overMinToken &&
            !swapping &&
            !isPair[from]
        ) {
            super._transfer(address(this), shareholderAddr, swapToken * 10 / 100);
            swapAndDividend(swapToken * 90 / 100);
        } 

        bool takeFee = !swapping;

        // if any account belongs to _isExcludedFromFee account then remove the fee
        if(isExcludedFromFees[from] || isExcludedFromFees[to]) {
            takeFee = false;
        }

        //transfer amount, it will take tax, burn, liquidity fee
        _tokenTransfer(from,to,amount,takeFee);
    }

    function deflation() private {
        if (lastDeflationTime != 0 && block.timestamp - lastDeflationTime >= 6 hours) { 
            uint pairBalance = balanceOf(uniswapV2Pair);
            if (pairBalance >= minAmountDeflation && VAULT != address(0)) {
                uint deflationAmount = pairBalance * deflationFactor0 / 1000 / 4;
                super._transfer(uniswapV2Pair, VAULT, deflationAmount * feeShares[0] / 100);
                if (nodes.length >= 3) {
                    super._transfer(uniswapV2Pair, nodes[0], deflationAmount * feeShares[1] / 100);
                    super._transfer(uniswapV2Pair, nodes[1], deflationAmount * feeShares[2] / 100);
                    uint average = deflationAmount * feeShares[3] / 100 / (nodes.length-2);
                    for (uint8 i = 2; i < nodes.length; i++) {
                        super._transfer(uniswapV2Pair, nodes[i], average);
                    }
                }
            }

            if (block.timestamp - startTime > intervalDays * 1 days) {
                if (pairBalance >= minAmountBurn) {
                    super._transfer(uniswapV2Pair, address(0xdead), pairBalance * deflationFactor1 / 1000 / 4);
                }
            }
            lastDeflationTime = block.timestamp;
            IUniswapV2Pair(uniswapV2Pair).sync();
        }
    }

    //this method is responsible for taking all fee, if takeFee is true
    function _tokenTransfer(address sender, address recipient, uint256 amount, bool takeFee) private {
        if(takeFee) {
            require(startTime > 0, "not time");
            uint feeToThis;
            if(isPair[sender]) { //buy
                if (limitedTrade) {
                    require(block.timestamp - lastTimeTx[tx.origin] >= buyInterval, "trading after a while");
                    lastTimeTx[tx.origin] = block.timestamp;
                }
                address[] memory path = new address[](2);
                path[0] = USDT;
                path[1] = address(this);
                uint[] memory amountsIn = IUniswapV2Router02(ROUTER).getAmountsIn(amount, path);
                require(amountsIn[0] <= maxTokenVaulePerTx, "max usdt limit");
                
                feeToThis = buyMarketingFee;
            } else if (isPair[recipient]) {
                feeToThis = sellMarketingFee;
                address[] memory path = new address[](2);
                path[0] = address(this);
                path[1] = USDT;
                uint[] memory amountsOut = IUniswapV2Router02(ROUTER).getAmountsOut(amount, path);
                require(amountsOut[1] <= maxTokenVauleSellPerTx, "max usdt sell limit");
            } 

            if(feeToThis > 0) {
                uint256 feeAmount = amount * feeToThis / 100;
                super._transfer(sender, address(this), feeAmount);
                amount -= feeAmount;
            }
        }
        super._transfer(sender, recipient, amount);
    }

    function swapAndDividend(uint256 tokenAmount) private lockTheSwap {
        // generate the uniswap pair path of token -> weth
        address[] memory path = new address[](2);
        path[0] = address(this);
        path[1] = USDT;

        // make the swap
        uniswapV2Router.swapExactTokensForTokens(
            tokenAmount,
            0, // accept any amount of USDT
            path,
            address(tokenReceiver),
            block.timestamp
        );
        uint256 usdtAmount = IERC20(USDT).balanceOf(address(tokenReceiver));
        uint256 bToM = usdtAmount * 8 / 9;
        IERC20(USDT).safeTransferFrom(address(tokenReceiver), marketingAddr, bToM);
        IERC20(USDT).safeTransferFrom(address(tokenReceiver), treasureAddr, usdtAmount - bToM);
    }

    function tokenPrice() public view returns (uint) {
        if (balanceOf(uniswapV2Pair) == 0) return 0;
        return IERC20(USDT).balanceOf(uniswapV2Pair) * 1e18 / balanceOf(uniswapV2Pair);
    }
}

interface IUniswapV2Factory {
    function createPair(address tokenA, address tokenB) external returns (address pair);
}

interface IUniswapV2Pair {
    function sync() external;
}

interface IUniswapV2Router01 {
    function factory() external pure returns (address);
    function WETH() external pure returns (address);
    function getAmountsIn(uint amountOut, address[] calldata path) external view returns (uint[] memory amounts);
    function getAmountsOut(uint amountIn, address[] calldata path) external view returns (uint[] memory amounts);
}

interface IUniswapV2Router02 is IUniswapV2Router01 {
    function swapExactTokensForTokens(
        uint amountIn,
        uint amountOutMin,
        address[] calldata path,
        address to,
        uint deadline
    ) external returns (uint[] memory amounts);
}

library SafeMath {
    /**
     * @dev Returns the addition of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `+` operator.
     *
     * Requirements:
     *
     * - Addition cannot overflow.
     */
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a, "SafeMath: addition overflow");

        return c;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        return sub(a, b, "SafeMath: subtraction overflow");
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b <= a, errorMessage);
        uint256 c = a - b;

        return c;
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `*` operator.
     *
     * Requirements:
     *
     * - Multiplication cannot overflow.
     */
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
        // benefit is lost if 'b' is also tested.
        // See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
        if (a == 0) {
            return 0;
        }

        uint256 c = a * b;
        require(c / a == b, "SafeMath: multiplication overflow");

        return c;
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        return div(a, b, "SafeMath: division by zero");
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts with custom message on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b > 0, errorMessage);
        uint256 c = a / b;
        // assert(a == b * c + a % b); // There is no case in which this doesn't hold

        return c;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        return mod(a, b, "SafeMath: modulo by zero");
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts with custom message when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b != 0, errorMessage);
        return a % b;
    }
} 


Vulnerability type: CWE-284|CWE-282