Problem p02623 (C++) — buggy submission, verdict: Runtime Error

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

// #define int long long
#define all(v) (v).begin(), (v).end()
#define rall(v) (v).rbegin(), (v).rend()
#define rep(i, n) for (int i = 0; i < n; ++i)
#define rep1(i, n) for (int i = 1; i < n; ++i)
#define exrep(i, a, b) for (ll i = a; i < b; i++)
#define out(x) cout << x << endl
#define EPS (1e-7)
#define gearup                                                                 \\
  ios_base::sync_with_stdio(0);                                                \\
  cin.tie(0);                                                                  \\
  cout.tie(0);

typedef long long ll;
typedef long double ld;
typedef unsigned long long ull;
typedef vector<int> vi;
typedef vector<char> vc;
typedef vector<bool> vb;
typedef vector<double> vd;
typedef vector<string> vs;
typedef vector<pair<int, int>> vpii;
typedef vector<vector<int>> vvi;
typedef vector<vector<char>> vvc;
typedef vector<vector<bool>> vvb;
typedef vector<vector<double>> vvd;
typedef vector<vector<string>> vvs;
typedef vector<ll> vl;
typedef vector<vector<ll>> vvl;
typedef vector<vector<vector<ll>>> vvvl;
ll MOD = 1000000007;
const long long L_INF = 1LL << 60;
const int INF = 2147483647; // 2^31-1
const double PI = acos(-1);
// cout<<fixed<<setprecision(10);

template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> void debug(T v) {
  rep(i, v.size()) cout << v[i] << " ";
  cout << endl;
}
const ll dx[8] = {1, 1, 0, -1, -1, -1, 0, 1};
const ll dy[8] = {0, 1, 1, 1, 0, -1, -1, -1};
// 以降 cin の入力元が 'input.txt' になる
// std::ifstream in("input.txt");
// std::cin.rdbuf(in.rdbuf());

signed main() {
  // 後ろから考える
  gearup;
  ll n, m, k;
  cin >> n >> m >> k;
  vl a(n), b(m);
  vl sa(n + 1), sb(m + 1);
  rep(i, n) cin >> a[i], sa[i + 1] = sa[i] + a[i];
  rep(i, m) cin >> b[i], sb[i + 1] = sb[i] + b[i];
  ll res = 0;
  rep(i, n + 1) {
    ll now = sa[i];
    ll dif = k - now;
    ll idx = upper_bound(all(sb), dif) - sb.begin();
    if (idx == 0)
      continue;
    res = max(res, (i) + idx - 1);
  }
  out(res);
}

Error: 0

Fixed submission:

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

// #define int long long
#define all(v) (v).begin(), (v).end()
#define rall(v) (v).rbegin(), (v).rend()
#define rep(i, n) for (int i = 0; i < n; ++i)
#define rep1(i, n) for (int i = 1; i < n; ++i)
#define exrep(i, a, b) for (ll i = a; i < b; i++)
#define out(x) cout << x << endl
#define EPS (1e-7)
#define gearup                                                                 \\
  ios_base::sync_with_stdio(0);                                                \\
  cin.tie(0);                                                                  \\
  cout.tie(0);

typedef long long ll;
typedef long double ld;
typedef unsigned long long ull;
typedef vector<int> vi;
typedef vector<char> vc;
typedef vector<bool> vb;
typedef vector<double> vd;
typedef vector<string> vs;
typedef vector<pair<int, int>> vpii;
typedef vector<vector<int>> vvi;
typedef vector<vector<char>> vvc;
typedef vector<vector<bool>> vvb;
typedef vector<vector<double>> vvd;
typedef vector<vector<string>> vvs;
typedef vector<ll> vl;
typedef vector<vector<ll>> vvl;
typedef vector<vector<vector<ll>>> vvvl;
ll MOD = 1000000007;
const long long L_INF = 1LL << 60;
const int INF = 2147483647; // 2^31-1
const double PI = acos(-1);
// cout<<fixed<<setprecision(10);

template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> void debug(T v) {
  rep(i, v.size()) cout << v[i] << " ";
  cout << endl;
}
const ll dx[8] = {1, 1, 0, -1, -1, -1, 0, 1};
const ll dy[8] = {0, 1, 1, 1, 0, -1, -1, -1};
// 以降 cin の入力元が 'input.txt' になる
// std::ifstream in("input.txt");
// std::cin.rdbuf(in.rdbuf());

signed main() {
  gearup;
  ll n, m, k;
  cin >> n >> m >> k;
  vl a(n), b(m);
  rep(i, n) cin >> a[i];
  rep(i, m) cin >> b[i];
  vl c(n + m);
  int a_idx = 0, b_idx = 0;
  int c_i = 0;
  while (a_idx < n && b_idx < n) {
    if (a[a_idx] <= b[b_idx])
      c[c_i++] = a[a_idx++];
    else
      c[c_i++] = b[b_idx++];
  }
  while (a_idx < n)
    c[c_i++] = a[a_idx++];
  while (b_idx < n)
    c[c_i++] = b[b_idx++];
  ll res = 0;
  ll t = 0;
  while (1) {
    // out(c[t]);
    if (t == n + m) {
      out(n + m);
      return 0;
    }
    if (res + c[t] <= k) {
      res += c[t++];
    } else {
      out(t);
      return 0;
    }
  }
}