Problem p03864 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <algorithm>
#include <cassert>
#include <climits>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstring>
#include <ctime>
#include <deque>
#include <iomanip>
#include <iostream>
#include <limits>
#include <list>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <utility>
#include <vector>
using namespace std;

#define rep(i, a, n) for (int i = a; i < n; i++)
#define repq(i, a, n) for (int i = a; i <= n; i++)
#define repr(i, a, n) for (int i = a; i >= n; i--)
#define pb(a) push_back(a)
#define fr first
#define sc second
#define INF 2000000000
#define int long long int

#define X real()
#define Y imag()
#define EPS (1e-10)
#define EQ(a, b) (abs((a) - (b)) < EPS)
#define EQV(a, b) (EQ((a).X, (b).X) && EQ((a).Y, (b).Y))
#define LE(n, m) ((n) < (m) + EPS)
#define LEQ(n, m) ((n) <= (m) + EPS)
#define GE(n, m) ((n) + EPS > (m))
#define GEQ(n, m) ((n) + EPS >= (m))

typedef vector<int> VI;
typedef vector<VI> MAT;
typedef pair<int, int> pii;
typedef long long ll;

typedef complex<double> P;
typedef pair<P, P> L;
typedef pair<P, double> C;

int dy[] = {0, 0, 1, -1};
int dx[] = {1, -1, 0, 0};
int const MOD = 1000000007;

namespace std {
bool operator<(const P &a, const P &b) {
  return a.X != b.X ? a.X < b.X : a.Y < b.Y;
}
} // namespace std

signed main() {
  int n, x;
  cin >> n >> x;
  int a[100010];
  rep(i, 0, n) cin >> a[i];
  int cnt = 0;
  rep(i, 0, n - 1) {
    while (a[i] + a[i + 1] > x) {
      if (a[i + 1] > 0)
        a[i + 1]--;
      else
        a[i]--;
      cnt++;
    }
  }
  cout << cnt << endl;
  return 0;
}

Fixed submission:
#include <algorithm>
#include <cassert>
#include <climits>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstring>
#include <ctime>
#include <deque>
#include <iomanip>
#include <iostream>
#include <limits>
#include <list>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <utility>
#include <vector>
using namespace std;

#define rep(i, a, n) for (int i = a; i < n; i++)
#define repq(i, a, n) for (int i = a; i <= n; i++)
#define repr(i, a, n) for (int i = a; i >= n; i--)
#define pb(a) push_back(a)
#define fr first
#define sc second
#define INF 2000000000
#define int long long int

#define X real()
#define Y imag()
#define EPS (1e-10)
#define EQ(a, b) (abs((a) - (b)) < EPS)
#define EQV(a, b) (EQ((a).X, (b).X) && EQ((a).Y, (b).Y))
#define LE(n, m) ((n) < (m) + EPS)
#define LEQ(n, m) ((n) <= (m) + EPS)
#define GE(n, m) ((n) + EPS > (m))
#define GEQ(n, m) ((n) + EPS >= (m))

typedef vector<int> VI;
typedef vector<VI> MAT;
typedef pair<int, int> pii;
typedef long long ll;

typedef complex<double> P;
typedef pair<P, P> L;
typedef pair<P, double> C;

int dy[] = {0, 0, 1, -1};
int dx[] = {1, -1, 0, 0};
int const MOD = 1000000007;

namespace std {
bool operator<(const P &a, const P &b) {
  return a.X != b.X ? a.X < b.X : a.Y < b.Y;
}
} // namespace std

signed main() {
  int n, x;
  cin >> n >> x;
  int a[100010];
  rep(i, 0, n) cin >> a[i];
  int cnt = 0;
  rep(i, 0, n - 1) {
    if (a[i] + a[i + 1] > x) {
      if (a[i] <= x) {
        int t = a[i + 1] - (x - a[i]);
        a[i + 1] -= t;
        cnt += t;
      } else {
        cnt += a[i + 1];
        a[i + 1] = 0;
        int t = a[i] - x;
        a[i] -= t;
        cnt += t;
      }
    }
  }
  cout << cnt << endl;
  return 0;
}