Problem p02959 (C++)

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

/* #pragma */
// #pragma GCC optimize("Ofast")
// #pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")

/*alias*/
#define F first
#define S second

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

/*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 */
int32_t GCD(int32_t a, int32_t b) { return b ? GCD(b, a % b) : a; }
int64_t GCD(int64_t a, int64_t b) { return b ? GCD(b, a % b) : a; }
int32_t LCM(int32_t a, int32_t b) { return a * b / GCD(a, b); }
int64_t LCM(int64_t a, int64_t b) { return a * b / GCD(a, b); }

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

/* const */
constexpr int32_t INF = 1001001001;
constexpr int64_t LINF = 1001001001001001001ll;
constexpr int32_t MOD = 1e9 + 7; // 10^9
constexpr int64_t EPS = 1e-9;
constexpr int32_t dx[] = {1, 1, 0, -1, -1, -1, 0, 1},
                  dy[] = {0, 1, 1, 1, 0, -1, -1, -1};
// constexpr int32_t dx[] = {1, 0, -1, 0}, dy[] = {0, 1, 0, -1};
// Counterclockwise from the 6o'clock direction
// Take the x-axis downward and the y-axis right

// g++ -std=c++14 -Wall --pedantic-errors -o template template.cpp
// g++ -std=c++14 -Wall --pedantic-errors template.cpp
// chcp 65001

/*global*/

#define int int64_t
signed main() {
  int n;
  cin >> n;
  vector<int> a(n + 1);
  for (int i = 0, i_len = (int)n + 1; i < i_len; ++i)
    cin >> a[i];

  vector<int> b(n);
  for (int i = 0, i_len = (int)n; i < i_len; ++i)
    cin >> b[i];

  int ans{};
  for (int i = 0, i_len = (int)n; i < i_len; ++i) {
    int left = min(a[i], b[i]);
    ans += left;
    a[i] -= left;
    b[i] -= left;

    int right = min(a[i + 1], b[i]);
    ans += right;
    a[i + 1] -= right;
    b[i + 1] -= right;
  }

  cout << ans << endl;
}

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

/* #pragma */
// #pragma GCC optimize("Ofast")
// #pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")

/*alias*/
#define F first
#define S second

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

/*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 */
int32_t GCD(int32_t a, int32_t b) { return b ? GCD(b, a % b) : a; }
int64_t GCD(int64_t a, int64_t b) { return b ? GCD(b, a % b) : a; }
int32_t LCM(int32_t a, int32_t b) { return a * b / GCD(a, b); }
int64_t LCM(int64_t a, int64_t b) { return a * b / GCD(a, b); }

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

/* const */
constexpr int32_t INF = 1001001001;
constexpr int64_t LINF = 1001001001001001001ll;
constexpr int32_t MOD = 1e9 + 7; // 10^9
constexpr int64_t EPS = 1e-9;
constexpr int32_t dx[] = {1, 1, 0, -1, -1, -1, 0, 1},
                  dy[] = {0, 1, 1, 1, 0, -1, -1, -1};
// constexpr int32_t dx[] = {1, 0, -1, 0}, dy[] = {0, 1, 0, -1};
// Counterclockwise from the 6o'clock direction
// Take the x-axis downward and the y-axis right

// g++ -std=c++14 -Wall --pedantic-errors -o template template.cpp
// g++ -std=c++14 -Wall --pedantic-errors template.cpp
// chcp 65001

/*global*/

#define int int64_t
signed main() {
  int n;
  cin >> n;
  vector<int> a(n + 1);
  for (int i = 0, i_len = (int)n + 1; i < i_len; ++i)
    cin >> a[i];

  vector<int> b(n);
  for (int i = 0, i_len = (int)n; i < i_len; ++i)
    cin >> b[i];

  int ans{};
  for (int i = 0, i_len = (int)n; i < i_len; ++i) {
    int left = min(a[i], b[i]);
    ans += left;
    a[i] -= left;
    b[i] -= left;

    int right = min(a[i + 1], b[i]);
    ans += right;
    a[i + 1] -= right;
    b[i] -= right;
  }

  cout << ans << endl;
}