Problem p03835 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <bits/stdc++.h>
#define FOR(i, m, n) for (int i = m; i < (n); i++)
#define RFOR(i, m, n) for (int i = (m - 1); i >= 0; i--)
#define REP(i, n) FOR(i, 0, n)
#define RREP(i, n) RFOR(i, n, 0)
#define ALL(v) v.begin(), v.end()
#define RALL(v) v.rbegin(), v.rend()
using namespace std;
typedef long long ll;
const int mod = 1e9 + 7;

ll gcd(ll x, ll y) { return y ? gcd(y, x % y) : x; }

ll factorial(ll n) {
  ll answer = 1;
  while (n > 1) {
    answer *= n;
    answer %= mod;
    n--;
  }
  return answer;
}

ll combination(ll n, ll r) {
  return factorial(n) / (factorial(r) * factorial(n - r));
}

ll permutation(ll n, ll r) { return factorial(n) / factorial(n - r); }

template <typename T> void remove(std::vector<T> &vector, unsigned int index) {
  vector.erase(vector.begin() + index);
}

map<ll, ll> prime_factor(ll n) {
  map<ll, ll> ret;
  for (ll i = 2; i * i <= n; i++) {
    while (n % i == 0) {
      ret[i]++;
      n /= i;
    }
  }
  if (n != 1)
    ret[n] = 1;
  return ret;
}
// for (auto p : prime_factor(n)) {
//	while (p.second--) {
//		cout << p.first << endl;
//	}
//}

vector<ll> divisor(ll n) {
  vector<ll> ret;
  for (ll i = 1; i * i <= n; i++) {
    if (n % i == 0) {
      ret.push_back(i);
      if (i * i != n)
        ret.push_back(n / i);
    }
  }
  sort(begin(ret), end(ret));
  return (ret);
}

int main() {
  int k, s;
  cin >> k >> s;
  int ans = 0;
  REP(x, k + 1) {
    REP(y, k + 1) {
      REP(z, k + 1) {
        if (x + y + z == s) {
          ans++;
        }
      }
    }
  }
  cout << ans << endl;
  return 0;
}

Fixed submission:
#include <bits/stdc++.h>
#define FOR(i, m, n) for (int i = m; i < (n); i++)
#define RFOR(i, m, n) for (int i = (m - 1); i >= 0; i--)
#define REP(i, n) FOR(i, 0, n)
#define RREP(i, n) RFOR(i, n, 0)
#define ALL(v) v.begin(), v.end()
#define RALL(v) v.rbegin(), v.rend()
using namespace std;
typedef long long ll;
const int mod = 1e9 + 7;

ll gcd(ll x, ll y) { return y ? gcd(y, x % y) : x; }

ll factorial(ll n) {
  ll answer = 1;
  while (n > 1) {
    answer *= n;
    answer %= mod;
    n--;
  }
  return answer;
}

ll combination(ll n, ll r) {
  return factorial(n) / (factorial(r) * factorial(n - r));
}

ll permutation(ll n, ll r) { return factorial(n) / factorial(n - r); }

template <typename T> void remove(std::vector<T> &vector, unsigned int index) {
  vector.erase(vector.begin() + index);
}

map<ll, ll> prime_factor(ll n) {
  map<ll, ll> ret;
  for (ll i = 2; i * i <= n; i++) {
    while (n % i == 0) {
      ret[i]++;
      n /= i;
    }
  }
  if (n != 1)
    ret[n] = 1;
  return ret;
}
// for (auto p : prime_factor(n)) {
//	while (p.second--) {
//		cout << p.first << endl;
//	}
//}

vector<ll> divisor(ll n) {
  vector<ll> ret;
  for (ll i = 1; i * i <= n; i++) {
    if (n % i == 0) {
      ret.push_back(i);
      if (i * i != n)
        ret.push_back(n / i);
    }
  }
  sort(begin(ret), end(ret));
  return (ret);
}

int main() {
  int k, s;
  cin >> k >> s;
  int ans = 0;
  REP(x, k + 1) {
    REP(y, k + 1) {
      int z = max(0, min(s - x - y, k));
      if (x + y + z == s) {
        ans++;
      }
    }
  }
  cout << ans << endl;
  return 0;
}