Problem p03835 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <bits/stdc++.h>
using namespace std;

/* REPmacro */
#define REP(i, n) for (int i = 0, i##_len = (n); i < i##_len; ++i)
#define REPR(i, n) for (int i = ((int)(n)-1); i >= 0; --i)
#define FOR(i, m, n) for (int i = (int)(m); i < (int)(n); ++i)

/*alias*/
#define ALL(x) (x).begin(), (x).end()
#define SZ(x) ((int)(x).size())
#define F first
#define S second
#define PB push_back
#define MP make_pair

#define y0 y3487465
#define y1 y8687969
#define j0 j1347829
#define j1 j234892
#define next asdnext
#define prev asdprev

/*using*/
using ll = long long;
using ull = unsigned long long;
using unsi = unsigned;
using vi = vector<int>;
using vvi = vector<vi>;
using vvvi = vector<vvi>;
using pii = pair<int, int>;
using db = double;
using plex = complex<double>;
using vs = vector<string>;

/*template*/
template <class T> inline bool amax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> inline bool amin(T &a, const T &b) {
  if (b < a) {
    a = b;
    return 1;
  }
  return 0;
}

/* func */
int gcd(int a, int b) { return b ? gcd(b, a % b) : a; }

/*struct*/
struct aaa {
  aaa() {
    cin.tie(0);
    ios::sync_with_stdio(0);
    cout << fixed << setprecision(20);
  };
} aaaaaaa;

/* const */
const int INF = 1001001001;
const ll LINF = 1001001001001001001ll;
const int MOD = 1e9 + 7; // 10^9
const db EPS = 1e-9;
const int dx[] = {0, 1, 0, -1, 1, -1, 1, -1},
          dy[] = {1, 0, -1, 0, 1, -1, -1, 1};

// #define int ll
// #define int long long

signed main() {
  int k, s;
  cin >> k >> s;
  int res = 0, cnt = 0;
  for (int x = 0; x <= k; ++x) {
    for (int y = 0; y <= k; ++y) {
      for (int z = 0; z <= k; ++z) {
        res = x + y + z;
        if (res == s)
          ++cnt;
      }
    }
  }

  cout << cnt;

  return 0;
}

Fixed submission:
#include <bits/stdc++.h>
using namespace std;

/* REPmacro */
#define REP(i, n) for (int i = 0, i##_len = (n); i < i##_len; ++i)
#define REPR(i, n) for (int i = ((int)(n)-1); i >= 0; --i)
#define FOR(i, m, n) for (int i = (int)(m); i < (int)(n); ++i)

/*alias*/
#define ALL(x) (x).begin(), (x).end()
#define SZ(x) ((int)(x).size())
#define F first
#define S second
#define PB push_back
#define MP make_pair

#define y0 y3487465
#define y1 y8687969
#define j0 j1347829
#define j1 j234892
#define next asdnext
#define prev asdprev

/*using*/
using ll = long long;
using ull = unsigned long long;
using unsi = unsigned;
using vi = vector<int>;
using vvi = vector<vi>;
using vvvi = vector<vvi>;
using pii = pair<int, int>;
using db = double;
using plex = complex<double>;
using vs = vector<string>;

/*template*/
template <class T> inline bool amax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> inline bool amin(T &a, const T &b) {
  if (b < a) {
    a = b;
    return 1;
  }
  return 0;
}

/* func */
int gcd(int a, int b) { return b ? gcd(b, a % b) : a; }

/*struct*/
struct aaa {
  aaa() {
    cin.tie(0);
    ios::sync_with_stdio(0);
    cout << fixed << setprecision(20);
  };
} aaaaaaa;

/* const */
const int INF = 1001001001;
const ll LINF = 1001001001001001001ll;
const int MOD = 1e9 + 7; // 10^9
const db EPS = 1e-9;
const int dx[] = {0, 1, 0, -1, 1, -1, 1, -1},
          dy[] = {1, 0, -1, 0, 1, -1, -1, 1};

// #define int ll
// #define int long long

signed main() {
  int k, s;
  cin >> k >> s;
  int res = 0, cnt = 0;
  for (int x = 0; x <= k; ++x) {
    for (int y = 0; y <= k; ++y) {
      int z = s - x - y;
      if (0 <= z && z <= k)
        ++cnt;
    }
  }

  cout << cnt;

  return 0;
}