Problem p02650 (C++) — buggy submission, verdict: Time Limit Exceeded

#include <bits/stdc++.h>
using namespace std;
// #pragma GCC optimize("Ofast")
// #pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")

#define ms(s, n) memset(s, n, sizeof(s))
#define FOR(i, a, b) for (int i = (a); i < (b); ++i)
#define FORd(i, a, b) for (int i = (a)-1; i >= (b); --i)
#define FORall(it, a)                                                          \\
  for (__typeof((a).begin()) it = (a).begin(); it != (a).end(); it++)
#define sz(a) int((a).size())
#define present(t, x) (t.find(x) != t.end())
#define all(a) (a).begin(), (a).end()
#define uni(a) (a).erase(unique(all(a)), (a).end())
#define pb push_back
#define pf push_front
#define mp make_pair
#define fi first
#define se second
#define prec(n) fixed << setprecision(n)
#define bit(n, i) (((n) >> (i)) & 1)
#define bitcount(n) __builtin_popcountll(n)
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
typedef pair<int, int> pi;
typedef vector<int> vi;
typedef vector<pi> vii;
const int MOD = (int)1e9 + 7;
const int FFTMOD = 119 << 23 | 1;
const int INF = (int)1e9 + 23111992;
const ll LINF = (ll)1e18 + 23111992;
const ld PI = acos((ld)-1);
const ld EPS = 1e-9;
inline ll gcd(ll a, ll b) {
  ll r;
  while (b) {
    r = a % b;
    a = b;
    b = r;
  }
  return a;
}
inline ll lcm(ll a, ll b) { return a / gcd(a, b) * b; }
inline ll fpow(ll n, ll k, int p = MOD) {
  ll r = 1;
  for (; k; k >>= 1) {
    if (k & 1)
      r = r * n % p;
    n = n * n % p;
  }
  return r;
}
template <class T> inline int chkmin(T &a, const T &val) {
  return val < a ? a = val, 1 : 0;
}
template <class T> inline int chkmax(T &a, const T &val) {
  return a < val ? a = val, 1 : 0;
}
inline ull isqrt(ull k) {
  ull r = sqrt(k) + 1;
  while (r * r > k)
    r--;
  return r;
}
inline ll icbrt(ll k) {
  ll r = cbrt(k) + 1;
  while (r * r * r > k)
    r--;
  return r;
}
inline void addmod(int &a, int val, int p = MOD) {
  if ((a = (a + val)) >= p)
    a -= p;
}
inline void submod(int &a, int val, int p = MOD) {
  if ((a = (a - val)) < 0)
    a += p;
}
inline int mult(int a, int b, int p = MOD) { return (ll)a * b % p; }
inline int inv(int a, int p = MOD) { return fpow(a, p - 2, p); }
inline int sign(ld x) { return x < -EPS ? -1 : x > +EPS; }
inline int sign(ld x, ld y) { return sign(x - y); }
mt19937 mt(chrono::high_resolution_clock::now().time_since_epoch().count());
inline int mrand() { return abs((int)mt()); }
inline int mrand(int k) { return abs((int)mt()) % k; }
#define db(x) cerr << "[" << #x << ": " << (x) << "] ";
#define endln cerr << "\\n";

void chemthan() {
  const int magic = 5000;
  vector<vi> dvs(magic);
  FOR(i, 1, sz(dvs)) {
    for (int j = i; j < sz(dvs); j += i) {
      dvs[j].pb(i);
    }
  }
  int w, h, d;
  cin >> w >> h >> d;
  vector<vi> g(magic, vi(magic));
  FOR(i, 0, magic) g[0][i] = g[i][0] = i;
  FOR(i, 1, magic) FOR(j, 1, magic) {
    if (i <= j)
      g[i][j] = g[i][j - i];
    else
      g[i][j] = g[i - j][j];
  }

  auto calc = [&](int x, int y) {
    if (!x || !y)
      return x + y - 1;
    x = abs(x), y = abs(y);
    if (y < x)
      swap(x, y);
    y %= x;
    if (x < magic && y < magic)
      return g[x][y] - 1;
    return __gcd(x, y) - 1;
  };

  long long res = 0;
  FOR(it, 0, 2) {
    vi f(1e6);
    FOR(i, 0, sz(f)) f[i] = __gcd(i, w) - 1;
    FOR(i, 1, w) if (i + i <= w) {
      for (int j = 1; j < h && i * j <= d + d + w + h + h; j++) {
        int t = d + d + calc(j, w - i) + 1 - i * j;
        //(w - i) * k - gcd(w, |j - k|) - gcd(i, k) <= t
        int c = 1 + (i + i < w);
        int s = min(h - 1, t < 0 ? 0 : t / (w - i));
        res += c * s;
        for (int k = s + 1; k < h; k++) {
          if ((w - i) * k < t + w + i) {
            if ((w - i) * k - f[abs(j - k)] - calc(i, k) <= t) {
              res += c;
            }
          } else {
            break;
          }
        }
      }
    }
    swap(w, h);
  }
  cout << res * 2 << "\\n";
}

int main(int argc, char *argv[]) {
  ios_base::sync_with_stdio(0), cin.tie(0);
  if (argc > 1) {
    assert(freopen(argv[1], "r", stdin));
  }
  if (argc > 2) {
    assert(freopen(argv[2], "wb", stdout));
  }
  chemthan();
  cerr << "\\nTime elapsed: " << 1000 * clock() / CLOCKS_PER_SEC << "ms\\n";
  return 0;
}


Error: TLE

Fixed submission:

#include <bits/stdc++.h>
using namespace std;
// #pragma GCC optimize("Ofast")
// #pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")

#define ms(s, n) memset(s, n, sizeof(s))
#define FOR(i, a, b) for (int i = (a); i < (b); ++i)
#define FORd(i, a, b) for (int i = (a)-1; i >= (b); --i)
#define FORall(it, a)                                                          \\
  for (__typeof((a).begin()) it = (a).begin(); it != (a).end(); it++)
#define sz(a) int((a).size())
#define present(t, x) (t.find(x) != t.end())
#define all(a) (a).begin(), (a).end()
#define uni(a) (a).erase(unique(all(a)), (a).end())
#define pb push_back
#define pf push_front
#define mp make_pair
#define fi first
#define se second
#define prec(n) fixed << setprecision(n)
#define bit(n, i) (((n) >> (i)) & 1)
#define bitcount(n) __builtin_popcountll(n)
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
typedef pair<int, int> pi;
typedef vector<int> vi;
typedef vector<pi> vii;
const int MOD = (int)1e9 + 7;
const int FFTMOD = 119 << 23 | 1;
const int INF = (int)1e9 + 23111992;
const ll LINF = (ll)1e18 + 23111992;
const ld PI = acos((ld)-1);
const ld EPS = 1e-9;
inline ll gcd(ll a, ll b) {
  ll r;
  while (b) {
    r = a % b;
    a = b;
    b = r;
  }
  return a;
}
inline ll lcm(ll a, ll b) { return a / gcd(a, b) * b; }
inline ll fpow(ll n, ll k, int p = MOD) {
  ll r = 1;
  for (; k; k >>= 1) {
    if (k & 1)
      r = r * n % p;
    n = n * n % p;
  }
  return r;
}
template <class T> inline int chkmin(T &a, const T &val) {
  return val < a ? a = val, 1 : 0;
}
template <class T> inline int chkmax(T &a, const T &val) {
  return a < val ? a = val, 1 : 0;
}
inline ull isqrt(ull k) {
  ull r = sqrt(k) + 1;
  while (r * r > k)
    r--;
  return r;
}
inline ll icbrt(ll k) {
  ll r = cbrt(k) + 1;
  while (r * r * r > k)
    r--;
  return r;
}
inline void addmod(int &a, int val, int p = MOD) {
  if ((a = (a + val)) >= p)
    a -= p;
}
inline void submod(int &a, int val, int p = MOD) {
  if ((a = (a - val)) < 0)
    a += p;
}
inline int mult(int a, int b, int p = MOD) { return (ll)a * b % p; }
inline int inv(int a, int p = MOD) { return fpow(a, p - 2, p); }
inline int sign(ld x) { return x < -EPS ? -1 : x > +EPS; }
inline int sign(ld x, ld y) { return sign(x - y); }
mt19937 mt(chrono::high_resolution_clock::now().time_since_epoch().count());
inline int mrand() { return abs((int)mt()); }
inline int mrand(int k) { return abs((int)mt()) % k; }
#define db(x) cerr << "[" << #x << ": " << (x) << "] ";
#define endln cerr << "\\n";

void chemthan() {
  int w, h, d;
  cin >> w >> h >> d;
  int magic = 5000;
  vector<vi> g(magic, vi(magic));
  FOR(i, 0, magic) g[0][i] = g[i][0] = i;
  FOR(i, 1, magic) FOR(j, 1, magic) {
    if (i <= j)
      g[i][j] = g[i][j - i];
    else
      g[i][j] = g[i - j][j];
  }

  auto calc = [&](int x, int y) {
    x = abs(x), y = abs(y);
    if (x < magic && y < magic)
      return g[x][y] - 1;
    return __gcd(x, y) - 1;
  };

  int res = 0;
  FOR(it, 0, 2) {
    vi f(1e6);
    FOR(i, 0, sz(f)) f[i] = __gcd(i, w) - 1;
    FOR(i, 1, w) if (i + i <= w) {
      for (int j = 1; j < h && i * j <= 2 * d + 3e5; j++) {
        int tmp = calc(j, w - i);
        int s;
        for (int k = 1;
             k < h && (s = abs(j * i + (w - i) * k) - tmp) <= 2 * d + 2e5;
             k++) {
          if (s <= d + d) {
            res += 2;
            if (i + i == w) {
              res--;
            }
          } else {
            s -= f[abs(j - k)];
            s -= calc(k, i);
            s -= 1;
            if (s <= d + d) {
              res += 2;
              if (i + i == w) {
                res--;
              }
            }
          }
        }
      }
    }
    swap(w, h);
  }
  cout << res * 2 << "\\n";
}

int main(int argc, char *argv[]) {
  ios_base::sync_with_stdio(0), cin.tie(0);
  if (argc > 1) {
    assert(freopen(argv[1], "r", stdin));
  }
  if (argc > 2) {
    assert(freopen(argv[2], "wb", stdout));
  }
  chemthan();
  cerr << "\\nTime elapsed: " << 1000 * clock() / CLOCKS_PER_SEC << "ms\\n";
  return 0;
}