Problem p03266 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <bits/stdc++.h>
#include <numeric>
#include <vector>
#define PI 3.14159265358979323846
#define MAXINF 1e18L
#define INF 1e9L
#define EPS 1e-9
#define REP(i, n) for (int i = 0; i < int(n); ++i)
#define Rep(i, sta, n) for (int i = sta; i < n; i++)
#define RREP(i, n) for (int i = int(n) - 1; i >= 0; --i)
#define ALL(v) v.begin(), v.end()
#define FIND(v, x) (binary_search(ALL(v), (x)))
#define SORT(v) sort(ALL(v))
#define RSORT(v)                                                               \
  sort(ALL(v));                                                                \
  reverse(ALL(v))
#define DEBUG(x) cerr << #x << ": " << x << endl;
#define DEBUG_VEC(v)                                                           \
  cerr << #v << ":";                                                           \
  for (int i = 0; i < v.size(); i++)                                           \
    cerr << " " << v[i];                                                       \
  cerr << endl
#define Yes(n) cout << ((n) ? "Yes" : "No") << endl
#define pb push_back
using namespace std;
template <class A> void pr(A a) { cout << (a) << endl; }
template <class A, class B> void pr(A a, B b) {
  cout << a << " ";
  pr(b);
}
template <class A, class B, class C> void pr(A a, B b, C c) {
  cout << a << " ";
  pr(b, c);
}
template <class A, class B, class C, class D> void pr(A a, B b, C c, D d) {
  cout << a << " ";
  pr(b, c, d);
}
typedef long long ll;
typedef pair<int, int> pii;
typedef tuple<int, int, int> tiii;

int n, k;

int main(void) {
  cin >> n >> k;
  int ans = 0;
  Rep(a, 1, n + 1) {
    for (int i = 1; 3 * n >= k * i; i++) {
      int b = k * i - a;
      if (b <= 0 || n < b)
        continue;
      for (int j = 1; 3 * n >= k * j; j++) {
        int c = k * j - a;
        if (c <= 0 || n < c)
          continue;
        if ((b + c) % k == 0)
          ans++;
      }
    }
  }
  pr(ans);
}

Fixed submission:
#include <bits/stdc++.h>
#include <numeric>
#include <vector>
#define PI 3.14159265358979323846
#define MAXINF 1e18L
#define INF 1e9L
#define EPS 1e-9
#define REP(i, n) for (int i = 0; i < int(n); ++i)
#define Rep(i, sta, n) for (int i = sta; i < n; i++)
#define RREP(i, n) for (int i = int(n) - 1; i >= 0; --i)
#define ALL(v) v.begin(), v.end()
#define FIND(v, x) (binary_search(ALL(v), (x)))
#define SORT(v) sort(ALL(v))
#define RSORT(v)                                                               \
  sort(ALL(v));                                                                \
  reverse(ALL(v))
#define DEBUG(x) cerr << #x << ": " << x << endl;
#define DEBUG_VEC(v)                                                           \
  cerr << #v << ":";                                                           \
  for (int i = 0; i < v.size(); i++)                                           \
    cerr << " " << v[i];                                                       \
  cerr << endl
#define Yes(n) cout << ((n) ? "Yes" : "No") << endl
#define pb push_back
using namespace std;
template <class A> void pr(A a) { cout << (a) << endl; }
template <class A, class B> void pr(A a, B b) {
  cout << a << " ";
  pr(b);
}
template <class A, class B, class C> void pr(A a, B b, C c) {
  cout << a << " ";
  pr(b, c);
}
template <class A, class B, class C, class D> void pr(A a, B b, C c, D d) {
  cout << a << " ";
  pr(b, c, d);
}
typedef long long ll;
typedef pair<int, int> pii;
typedef tuple<int, int, int> tiii;

int n, k;

int main(void) {
  cin >> n >> k;
  ll ans = 0;
  if (k % 2 != 0) {
    ll a = n / k;
    ans = pow(a, 3);
  } else {
    ll a = n / k;
    ll b = (2 * n / k) - a;
    ans = pow(a, 3) + pow(b, 3);
  }
  pr(ans);
}