Problem p02584 (C++)

Buggy submission (status: Time Limit Exceeded):
// HEADER FILES AND NAMESPACES

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;

template <typename T>
using ordered_set =
    tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;

template <typename T>
using ordered_multiset = tree<T, null_type, less_equal<T>, rb_tree_tag,
                              tree_order_statistics_node_update>;

// DEFINE STATEMENTS
const long long infty = 1e18;
#define num1 1000000007
#define num2 998244353
#define REP(i, a, n) for (ll i = a; i < n; i++)
#define REPd(i, a, n) for (ll i = a; i >= n; i--)
#define pb push_back
#define pob pop_back
#define f first
#define s second
#define fix(f, n) std::fixed << std::setprecision(n) << f
#define all(x) x.begin(), x.end()
#define M_PI 3.14159265358979323846
#define epsilon (double)(0.000000001)

typedef long long ll;
typedef vector<long long> vll;
typedef pair<long long, long long> pll;
typedef vector<pair<long long, long long>> vpll;
typedef vector<int> vii;

// DEBUG FUNCTIONS
#ifndef ONLINE_JUDGE

template <typename T> void __p(T a) { cout << a; }
template <typename T, typename F> void __p(pair<T, F> a) {
  cout << "{";
  __p(a.first);
  cout << ",";
  __p(a.second);
  cout << "}";
}
template <typename T> void __p(std::vector<T> a) {
  cout << "{";
  for (auto it = a.begin(); it < a.end(); it++)
    __p(*it), cout << ",}"[it + 1 == a.end()];
}
template <typename T> void __p(std::set<T> a) {
  cout << "{";
  for (auto it = a.begin(); it != a.end();) {
    __p(*it);
    cout << ",}"[++it == a.end()];
  }
}
template <typename T> void __p(std::multiset<T> a) {
  cout << "{";
  for (auto it = a.begin(); it != a.end();) {
    __p(*it);
    cout << ",}"[++it == a.end()];
  }
}
template <typename T, typename F> void __p(std::map<T, F> a) {
  cout << "{\n";
  for (auto it = a.begin(); it != a.end(); ++it) {
    __p(it->first);
    cout << ": ";
    __p(it->second);
    cout << "\n";
  }
  cout << "}\n";
}

template <typename T, typename... Arg> void __p(T a1, Arg... a) {
  __p(a1);
  __p(a...);
}
template <typename Arg1> void __f(const char *name, Arg1 &&arg1) {
  cout << name << " : ";
  __p(arg1);
  cout << endl;
}
template <typename Arg1, typename... Args>
void __f(const char *names, Arg1 &&arg1, Args &&...args) {
  int bracket = 0, i = 0;
  for (;; i++)
    if (names[i] == ',' && bracket == 0)
      break;
    else if (names[i] == '(')
      bracket++;
    else if (names[i] == ')')
      bracket--;
  const char *comma = names + i;
  cout.write(names, comma - names) << " : ";
  __p(arg1);
  cout << " | ";
  __f(comma + 1, args...);
}
#define trace(...)                                                             \
  cout << "Line:" << __LINE__ << " ", __f(#__VA_ARGS__, __VA_ARGS__)
#else
#define trace(...)
#define error(...)
#endif

// DEBUG FUNCTIONS END

// CUSTOM HASH TO SPEED UP UNORDERED MAP AND TO AVOID FORCED CLASHES
struct custom_hash {
  static uint64_t splitmix64(uint64_t x) {
    x += 0x9e3779b97f4a7c15;
    x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9;
    x = (x ^ (x >> 27)) * 0x94d049bb133111eb;
    return x ^ (x >> 31);
  }

  size_t operator()(uint64_t x) const {
    static const uint64_t FIXED_RANDOM =
        chrono::steady_clock::now().time_since_epoch().count();
    return splitmix64(x + FIXED_RANDOM);
  }
};

mt19937_64 rng(chrono::steady_clock::now()
                   .time_since_epoch()
                   .count()); // FOR RANDOM NUMBER GENERATION

ll mod_exp(ll a, ll b, ll c) {
  ll res = 1;
  a = a % c;
  while (b > 0) {
    if (b % 2 == 1)
      res = (res * a) % c;
    b /= 2;
    a = (a * a) % c;
  }
  return res;
}
ll mymod(ll a, ll b) { return ((a % b) + b) % b; }
ll gcdExtended(ll, ll, ll *, ll *);
ll modInverse(ll a, ll m) {
  ll x, y;
  ll g = gcdExtended(a, m, &x, &y);
  g++; // this line was added just to remove compiler warning
  ll res = (x % m + m) % m;
  return res;
}
ll gcdExtended(ll a, ll b, ll *x, ll *y) {
  if (a == 0) {
    *x = 0, *y = 1;
    return b;
  }
  ll x1, y1;
  ll gcd = gcdExtended(b % a, a, &x1, &y1);
  *x = y1 - (b / a) * x1;
  *y = x1;
  return gcd;
}
bool my(pair<pll, ll> p1, pair<pll, ll> p2) {
  if (p1.f.f < p2.f.f)
    return true;
  else if (p1.f.f == p2.f.f && p1.s < p2.s)
    return true;
  return false;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  ll x, k, d;
  cin >> x >> k >> d;
  while (x >= d && k > 0) {
    x -= d;
    k--;
  }
  while (x <= -d && k > 0) {
    x += d;
    k--;
  }
  if (!k) {
    cout << abs(x) << "\n";
    exit(0);
  }
  if (k & 1) {
    if (x >= 0) {
      cout << abs(x - d) << "\n";
    } else {
      cout << x + d << "\n";
    }
  } else {
    cout << abs(x) << "\n";
  }

  return 0;
}

/*
1. Check borderline constraints. Can a variable you are dividing by be 0?
2. Use ll while using bitshifts
3. Do not erase from set while iterating it
4. Initialise everything
5. Read the task carefully, is something unique, sorted, adjacent, guaranteed??
6. DO NOT use if(!mp[x]) if you want to iterate the map later
7. Are you using i in all loops? Are the i's conflicting?
*/

Fixed submission:
// HEADER FILES AND NAMESPACES

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;

template <typename T>
using ordered_set =
    tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;

template <typename T>
using ordered_multiset = tree<T, null_type, less_equal<T>, rb_tree_tag,
                              tree_order_statistics_node_update>;

// DEFINE STATEMENTS
const long long infty = 1e18;
#define num1 1000000007
#define num2 998244353
#define REP(i, a, n) for (ll i = a; i < n; i++)
#define REPd(i, a, n) for (ll i = a; i >= n; i--)
#define pb push_back
#define pob pop_back
#define f first
#define s second
#define fix(f, n) std::fixed << std::setprecision(n) << f
#define all(x) x.begin(), x.end()
#define M_PI 3.14159265358979323846
#define epsilon (double)(0.000000001)

typedef long long ll;
typedef vector<long long> vll;
typedef pair<long long, long long> pll;
typedef vector<pair<long long, long long>> vpll;
typedef vector<int> vii;

// DEBUG FUNCTIONS
#ifndef ONLINE_JUDGE

template <typename T> void __p(T a) { cout << a; }
template <typename T, typename F> void __p(pair<T, F> a) {
  cout << "{";
  __p(a.first);
  cout << ",";
  __p(a.second);
  cout << "}";
}
template <typename T> void __p(std::vector<T> a) {
  cout << "{";
  for (auto it = a.begin(); it < a.end(); it++)
    __p(*it), cout << ",}"[it + 1 == a.end()];
}
template <typename T> void __p(std::set<T> a) {
  cout << "{";
  for (auto it = a.begin(); it != a.end();) {
    __p(*it);
    cout << ",}"[++it == a.end()];
  }
}
template <typename T> void __p(std::multiset<T> a) {
  cout << "{";
  for (auto it = a.begin(); it != a.end();) {
    __p(*it);
    cout << ",}"[++it == a.end()];
  }
}
template <typename T, typename F> void __p(std::map<T, F> a) {
  cout << "{\n";
  for (auto it = a.begin(); it != a.end(); ++it) {
    __p(it->first);
    cout << ": ";
    __p(it->second);
    cout << "\n";
  }
  cout << "}\n";
}

template <typename T, typename... Arg> void __p(T a1, Arg... a) {
  __p(a1);
  __p(a...);
}
template <typename Arg1> void __f(const char *name, Arg1 &&arg1) {
  cout << name << " : ";
  __p(arg1);
  cout << endl;
}
template <typename Arg1, typename... Args>
void __f(const char *names, Arg1 &&arg1, Args &&...args) {
  int bracket = 0, i = 0;
  for (;; i++)
    if (names[i] == ',' && bracket == 0)
      break;
    else if (names[i] == '(')
      bracket++;
    else if (names[i] == ')')
      bracket--;
  const char *comma = names + i;
  cout.write(names, comma - names) << " : ";
  __p(arg1);
  cout << " | ";
  __f(comma + 1, args...);
}
#define trace(...)                                                             \
  cout << "Line:" << __LINE__ << " ", __f(#__VA_ARGS__, __VA_ARGS__)
#else
#define trace(...)
#define error(...)
#endif

// DEBUG FUNCTIONS END

// CUSTOM HASH TO SPEED UP UNORDERED MAP AND TO AVOID FORCED CLASHES
struct custom_hash {
  static uint64_t splitmix64(uint64_t x) {
    x += 0x9e3779b97f4a7c15;
    x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9;
    x = (x ^ (x >> 27)) * 0x94d049bb133111eb;
    return x ^ (x >> 31);
  }

  size_t operator()(uint64_t x) const {
    static const uint64_t FIXED_RANDOM =
        chrono::steady_clock::now().time_since_epoch().count();
    return splitmix64(x + FIXED_RANDOM);
  }
};

mt19937_64 rng(chrono::steady_clock::now()
                   .time_since_epoch()
                   .count()); // FOR RANDOM NUMBER GENERATION

ll mod_exp(ll a, ll b, ll c) {
  ll res = 1;
  a = a % c;
  while (b > 0) {
    if (b % 2 == 1)
      res = (res * a) % c;
    b /= 2;
    a = (a * a) % c;
  }
  return res;
}
ll mymod(ll a, ll b) { return ((a % b) + b) % b; }
ll gcdExtended(ll, ll, ll *, ll *);
ll modInverse(ll a, ll m) {
  ll x, y;
  ll g = gcdExtended(a, m, &x, &y);
  g++; // this line was added just to remove compiler warning
  ll res = (x % m + m) % m;
  return res;
}
ll gcdExtended(ll a, ll b, ll *x, ll *y) {
  if (a == 0) {
    *x = 0, *y = 1;
    return b;
  }
  ll x1, y1;
  ll gcd = gcdExtended(b % a, a, &x1, &y1);
  *x = y1 - (b / a) * x1;
  *y = x1;
  return gcd;
}
bool my(pair<pll, ll> p1, pair<pll, ll> p2) {
  if (p1.f.f < p2.f.f)
    return true;
  else if (p1.f.f == p2.f.f && p1.s < p2.s)
    return true;
  return false;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  ll x, k, d;
  cin >> x >> k >> d;
  if (x >= d) {
    ll times = min(x / d, k);
    x -= times * d;
    k -= times;
  }
  if (x <= -d) {
    ll times = min(abs(x) / d, k);
    x += times * d;
    k -= times;
  }
  if (!k) {
    cout << abs(x) << "\n";
    exit(0);
  }
  if (k & 1) {
    if (x >= 0) {
      cout << abs(x - d) << "\n";
    } else {
      cout << x + d << "\n";
    }
  } else {
    cout << abs(x) << "\n";
  }

  return 0;
}

/*
1. Check borderline constraints. Can a variable you are dividing by be 0?
2. Use ll while using bitshifts
3. Do not erase from set while iterating it
4. Initialise everything
5. Read the task carefully, is something unique, sorted, adjacent, guaranteed??
6. DO NOT use if(!mp[x]) if you want to iterate the map later
7. Are you using i in all loops? Are the i's conflicting?
*/