Problem p02584 (C++) — buggy submission, verdict: Time Limit Exceeded

#include <bits/stdc++.h>
#pragma GCC optimize("Ofast")
using namespace std;
typedef long long ll;
typedef pair<ll, ll> PLL;
typedef vector<int> VI;
typedef vector<char> VC;
typedef vector<double> VD;
typedef vector<string> VS;
typedef vector<ll> VLL;
typedef vector<PLL> VP;
const static int INF = 1000000000;
const static int MOD = 1000000007;
const int dx[4] = {1, 0, -1, 0};
const int dy[4] = {0, 1, 0, -1};
template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
#define rep(i, n) for (ll i = 0; i < (ll)(n); i++)
#define repd(i, n) for (ll i = n - 1; i >= 0; i--)
#define rept(i, m, n) for (ll i = m; i < n; i++)
#define stl_rep(itr, x) for (auto itr = x.begin(); itr != x.end(); ++itr)
#define all(x) (x).begin(), (x).end()
#define F first
#define S second
#define PF push_front
#define PB push_back
#define SORT(V) sort((V).begin(), (V).end())
#define RVERSE(V) reverse((V).begin(), (V).end())
#define paired make_pair
#define PRINT(V)                                                               \\
  for (auto v : (V))                                                           \\
  cout << v << " "
// charを整数に
int ctoi(char c) {
  if (c >= '0' && c <= '9') {
    return c - '0';
  }
  return 0;
}
// 累積和 for (int i = 0; i < N; ++i) s[i+1] = s[i] + a[i];
void cum_sum(int N, vector<double> a, vector<double> &s) {
  for (int i = 0; i < N; i++) {
    s[i + 1] = s[i] + a[i];
  }
}
// ユークリッドの控除法
ll gcd(ll a, ll b) {
  if (b == 0)
    return a;
  return gcd(b, a % b);
}
// 最小公倍数
ll lcm(ll a, ll b) {
  ll g = gcd(a, b);
  return a / g * b; // Be careful not to overflow
}
// 素数判定
bool is_prime(long long n) {
  if (n <= 1)
    return false;
  for (long long p = 2; p * p <= n; ++p) {
    if (n % p == 0)
      return false;
  }
  return true;
}
int getdigit(ll num) {
  unsigned digit = 0;
  while (num != 0) {
    num /= 10;
    digit++;
  }
  return digit;
}
// 空白文字も入力 getline(cin, S);
// 桁数指定 setprecision

int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  ll X, K, D;
  cin >> X >> K >> D;
  X = abs(X);
  ll ans = 0;
  ll times = abs(X) / abs(D);
  if (times > K) {
    ans = X - D * K;
  } else {
    ll e = times;
    K -= e;
    X -= e * D;
    if (K % 2 == 0) {
      ans = X;
    } else {
      ans = abs(X - D);
    }
  }
  cout << ans << endl;
}


Error: TLE

Fixed submission:

#include <bits/stdc++.h>
#pragma GCC optimize("Ofast")
using namespace std;
typedef long long ll;
typedef pair<ll, ll> PLL;
typedef vector<int> VI;
typedef vector<char> VC;
typedef vector<double> VD;
typedef vector<string> VS;
typedef vector<ll> VLL;
typedef vector<PLL> VP;
const static int INF = 1000000000;
const static int MOD = 1000000007;
const int dx[4] = {1, 0, -1, 0};
const int dy[4] = {0, 1, 0, -1};
template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
#define rep(i, n) for (ll i = 0; i < (ll)(n); i++)
#define repd(i, n) for (ll i = n - 1; i >= 0; i--)
#define rept(i, m, n) for (ll i = m; i < n; i++)
#define stl_rep(itr, x) for (auto itr = x.begin(); itr != x.end(); ++itr)
#define all(x) (x).begin(), (x).end()
#define F first
#define S second
#define PF push_front
#define PB push_back
#define SORT(V) sort((V).begin(), (V).end())
#define RVERSE(V) reverse((V).begin(), (V).end())
#define paired make_pair
#define PRINT(V)                                                               \\
  for (auto v : (V))                                                           \\
  cout << v << " "
// charを整数に
int ctoi(char c) {
  if (c >= '0' && c <= '9') {
    return c - '0';
  }
  return 0;
}
// 累積和 for (int i = 0; i < N; ++i) s[i+1] = s[i] + a[i];
void cum_sum(int N, vector<double> a, vector<double> &s) {
  for (int i = 0; i < N; i++) {
    s[i + 1] = s[i] + a[i];
  }
}
// ユークリッドの控除法
ll gcd(ll a, ll b) {
  if (b == 0)
    return a;
  return gcd(b, a % b);
}
// 最小公倍数
ll lcm(ll a, ll b) {
  ll g = gcd(a, b);
  return a / g * b; // Be careful not to overflow
}
// 素数判定
bool is_prime(long long n) {
  if (n <= 1)
    return false;
  for (long long p = 2; p * p <= n; ++p) {
    if (n % p == 0)
      return false;
  }
  return true;
}
int getdigit(ll num) {
  unsigned digit = 0;
  while (num != 0) {
    num /= 10;
    digit++;
  }
  return digit;
}
// 空白文字も入力 getline(cin, S);
// 桁数指定 setprecision

int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  ll X, K, D;
  cin >> X >> K >> D;
  ll distance = abs(X);
  while (1) {
    if (distance <= 0)
      break;
    if (K == 0)
      break;
    distance -= D;
    K--;
  }
  distance = abs(distance);
  ll ans1 = 0;
  ll ans2 = 0;
  if (K % 2 == 0) {
    ans1 = distance;
  } else {
    ans1 = abs(distance - D);
  }
  cout << ans1 << endl;
}