Problem p03835 (C++)

Buggy submission (status: Time Limit Exceeded):
#pragma region _head

#include <algorithm>
#include <cmath>
#include <iomanip>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <regex>
#include <set>
#include <stack>
#include <string>
#include <utility>
#include <vector>

void Init() {
  std::cin.tie(0);
  std::ios::sync_with_stdio(false);
  struct Init_caller {
    Init_caller() { Init(); }
  } caller;
}

#pragma region _define

#define int LL
#define f(i, a, b) for (LL i = a; i < b; i++)
#define rep(i, n) for (LL i = 0; i < n; i++)
#define rep2(i, j, a, h, w)                                                    \
  for (LL i = 0; i < h; i++)                                                   \
    for (LL j = 0; j < w; j++)                                                 \
  cin >> a[i][j]
#define f_vI(v, n) f(i, 0, n) cin >> v[i]
#define f_v2I(v1, v2, n) f(i, 0, n) cin >> v1[i] >> v2[i]
#define f_v3I(v1, v2, v3, n) f(i, 0, n) cin >> v1[i] >> v2[i] >> v3[i]
#define f_vO(v, n) f(i, 0, n) cout << v[i] << endl
#define ei else if
#define all(a) a.begin(), a.end()
#define size(s) ((LL)s.size())
#define F first
#define S second
#define check() cout << "! ! !"
#define endl "\n"
#define _y() cout << "Yes" << endl
#define _Y() cout << "YES" << endl
#define _n() cout << "No" << endl
#define _N() cout << "NO" << endl
#define INT_INF 1 << 29
#define LL_INF 1LL << 60
#define MOD 1000000007

#pragma endregion

#pragma region _using

using namespace std;

using LL = long long;
using st = string;
using vi = vector<LL>;
using vvi = vector<vi>;
using vvvi = vector<vvi>;
using vd = vector<double>;
using vvd = vector<vd>;
using vvvd = vector<vvd>;
using vc = vector<char>;
using vvc = vector<vc>;
using vs = vector<st>;
using vb = vector<bool>;
using vvb = vector<vb>;
using vvvb = vector<vvb>;
using qi = queue<LL>;
using qc = queue<char>;
using qs = queue<st>;
using si = stack<LL>;
using sc = stack<char>;
using ss = stack<st>;
using pi = pair<LL, LL>;
using ppi = pair<pi, LL>;
using mll = map<LL, LL>;
using mcl = map<char, LL>;
using vpi = vector<pi>;
using vppi = vector<ppi>;

#pragma endregion

struct edge {
  int f, t, c; // from, to, cost
};

void y_n(bool p) { p ? _y() : _n(); }

void Y_N(bool p) { p ? _Y() : _N(); }

LL vmax(vi v, LL n) {
  int MAX = 0;
  f(i, 0, n) { MAX = max(MAX, v[i]); }
  return MAX;
}

LL vmin(vi v, LL n) {
  int MIN = LL_INF;
  f(i, 0, n) { MIN = min(MIN, v[i]); }
  return MIN;
}

LL gcd(LL a, LL b) {
  if (b == 0) {
    swap(a, b);
  }
  LL r;
  while ((r = a % b) != 0) {
    a = b;
    b = r;
  }
  return b;
}
LL lcm(LL a, LL b) { return (a / gcd(a, b) * b); }

// 素数判定
bool is_prime(int n) {
  for (int i = 2; i * i <= n; i++) {
    if (n % i == 0) {
      return false;
    }
  }
  return true;
}

// 素因数分解
void dec_prime(int n) {
  int a = 2;
  while (a * a <= n) {
    if (n % a == 0) {
      cout << a << endl;
      n /= a;
    } else {
      a++;
    }
  }
  cout << n << endl;
}

// エラトステネスの篩
void sieve_prime(LL n) {
  vb s(n + 1, true);
  f(i, 2, n + 1) {
    for (int j = 2; i * j <= n; j++) {
      s[i * j] = false;
    }
  }
  cout << "2から" << n << "までの素数" << endl;
  f(i, 2, n + 1) {
    if (s[i]) {
      cout << i << " ";
    }
  }
}

// 階乗計算
LL factorial(LL n) {
  LL a = 1, ret = 1;
  while (a < n) {
    a++;
    ret *= a;
    ret %= MOD;
  }
  return ret;
}

#pragma endregion

/*****************************************************************************/
signed 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;
  return 0;
}

Fixed submission:
#pragma region _head

#include <algorithm>
#include <cmath>
#include <iomanip>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <regex>
#include <set>
#include <stack>
#include <string>
#include <utility>
#include <vector>

void Init() {
  std::cin.tie(0);
  std::ios::sync_with_stdio(false);
  struct Init_caller {
    Init_caller() { Init(); }
  } caller;
}

#pragma region _define

#define int LL
#define f(i, a, b) for (LL i = a; i < b; i++)
#define rep(i, n) for (LL i = 0; i < n; i++)
#define rep2(i, j, a, h, w)                                                    \
  for (LL i = 0; i < h; i++)                                                   \
    for (LL j = 0; j < w; j++)                                                 \
  cin >> a[i][j]
#define f_vI(v, n) f(i, 0, n) cin >> v[i]
#define f_v2I(v1, v2, n) f(i, 0, n) cin >> v1[i] >> v2[i]
#define f_v3I(v1, v2, v3, n) f(i, 0, n) cin >> v1[i] >> v2[i] >> v3[i]
#define f_vO(v, n) f(i, 0, n) cout << v[i] << endl
#define ei else if
#define all(a) a.begin(), a.end()
#define size(s) ((LL)s.size())
#define F first
#define S second
#define check() cout << "! ! !"
#define endl "\n"
#define _y() cout << "Yes" << endl
#define _Y() cout << "YES" << endl
#define _n() cout << "No" << endl
#define _N() cout << "NO" << endl
#define INT_INF 1 << 29
#define LL_INF 1LL << 60
#define MOD 1000000007

#pragma endregion

#pragma region _using

using namespace std;

using LL = long long;
using st = string;
using vi = vector<LL>;
using vvi = vector<vi>;
using vvvi = vector<vvi>;
using vd = vector<double>;
using vvd = vector<vd>;
using vvvd = vector<vvd>;
using vc = vector<char>;
using vvc = vector<vc>;
using vs = vector<st>;
using vb = vector<bool>;
using vvb = vector<vb>;
using vvvb = vector<vvb>;
using qi = queue<LL>;
using qc = queue<char>;
using qs = queue<st>;
using si = stack<LL>;
using sc = stack<char>;
using ss = stack<st>;
using pi = pair<LL, LL>;
using ppi = pair<pi, LL>;
using mll = map<LL, LL>;
using mcl = map<char, LL>;
using vpi = vector<pi>;
using vppi = vector<ppi>;

#pragma endregion

struct edge {
  int f, t, c; // from, to, cost
};

void y_n(bool p) { p ? _y() : _n(); }

void Y_N(bool p) { p ? _Y() : _N(); }

LL vmax(vi v, LL n) {
  int MAX = 0;
  f(i, 0, n) { MAX = max(MAX, v[i]); }
  return MAX;
}

LL vmin(vi v, LL n) {
  int MIN = LL_INF;
  f(i, 0, n) { MIN = min(MIN, v[i]); }
  return MIN;
}

LL gcd(LL a, LL b) {
  if (b == 0) {
    swap(a, b);
  }
  LL r;
  while ((r = a % b) != 0) {
    a = b;
    b = r;
  }
  return b;
}
LL lcm(LL a, LL b) { return (a / gcd(a, b) * b); }

// 素数判定
bool is_prime(int n) {
  for (int i = 2; i * i <= n; i++) {
    if (n % i == 0) {
      return false;
    }
  }
  return true;
}

// 素因数分解
void dec_prime(int n) {
  int a = 2;
  while (a * a <= n) {
    if (n % a == 0) {
      cout << a << endl;
      n /= a;
    } else {
      a++;
    }
  }
  cout << n << endl;
}

// エラトステネスの篩
void sieve_prime(LL n) {
  vb s(n + 1, true);
  f(i, 2, n + 1) {
    for (int j = 2; i * j <= n; j++) {
      s[i * j] = false;
    }
  }
  cout << "2から" << n << "までの素数" << endl;
  f(i, 2, n + 1) {
    if (s[i]) {
      cout << i << " ";
    }
  }
}

// 階乗計算
LL factorial(LL n) {
  LL a = 1, ret = 1;
  while (a < n) {
    a++;
    ret *= a;
    ret %= MOD;
  }
  return ret;
}

#pragma endregion

/*****************************************************************************/
signed main() {
  int k, s;
  cin >> k >> s;
  int ans = 0;
  rep(x, k + 1) {
    rep(y, k + 1) {
      if (s - k <= x + y && x + y <= s) {
        ans++;
      }
    }
  }
  cout << ans;
  return 0;
}