Problem p02623 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using P = pair<int, int>;
using vl = vector<ll>;
using vvl = vector<vl>;
#define mp make_pair
#define pb push_back
#define _overload3(_1, _2, _3, name, ...) name
#define _rep(i, n) repi(i, 0, n)
#define repi(i, a, b) for (int i = int(a); i < int(b); i++)
#define rep(...) _overload3(__VA_ARGS__, repi, _rep, )(__VA_ARGS__)
#define rrep(i, n) for (int i = (n - 1); i >= 0; i--)
#define all(v) v.begin(), v.end()
#define sz(v) (int)((v).size())
#define MAX(v) *max_element(all(v))
#define MIN(v) *min_element(all(v))
#define Sort(v) sort(all(v))
#define Rev(v) reverse(all(v))
#define vec(type, name, ...) vector<type> name(__VA_ARGS__)
#define VEC(type, name, size)                                                  \
  vector<type> name(size);                                                     \
  in(name)
#define vv(type, name, h, ...)                                                 \
  vector<vector<type>> name(h, vector<type>(__VA_ARGS__))
#define VV(type, name, h, w)                                                   \
  vector<vector<type>> name(h, vector<type>(w));                               \
  in(name)
void debug_out() { cout << endl; }
template <typename Head, typename... Tail> void debug_out(Head H, Tail... T) {
  cout << H << " ";
  debug_out(T...);
}
#ifdef _DEBUG
#define debug(...) debug_out(__VA_ARGS__)
#else
#define debug(...)
#endif
template <typename T>
std::ostream &operator<<(std::ostream &os, std::vector<T> vec) {
  for (std::size_t i = 0; i < vec.size(); i++)
    os << vec[i] << (i + 1 == vec.size() ? "" : " ");
  return os;
}
inline void IN(void) { return; }
template <typename First, typename... Rest>
void IN(First &first, Rest &...rest) {
  cin >> first;
  IN(rest...);
  return;
}
template <class T> bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> bool chmin(T &a, const T &b) {
  if (b < a) {
    a = b;
    return 1;
  }
  return 0;
}
const ll INF = 1LL << 60;
const ll mod = 1000000007;
const int dx[8] = {1, 0, -1, 0, 1, 1, -1, -1};
const int dy[8] = {0, 1, 0, -1, 1, 1, -1, -1};

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  ll n, m, k;
  cin >> n >> m >> k;
  vector<ll> a(n), b(m);
  rep(i, n) cin >> a[i];
  rep(i, m) cin >> b[i];
  vector<ll> sa(n), sb(m);
  rep(i, n) sa[i + 1] = sa[i] + a[i];
  rep(i, m) sb[i + 1] = sb[i] + b[i];

  ll ans = 0;
  rep(i, n + 1) {
    if (sa[i] > k)
      continue;
    ll ok = 0, ng = m + 1;
    while (abs(ok - ng) > 1) {
      ll mid = (ok + ng) / 2;
      if (sa[i] + sb[mid] <= k)
        ok = mid;
      else
        ng = mid;
    }
    chmax(ans, i + ok);
  }
  cout << ans << endl;
}

Fixed submission:
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using P = pair<int, int>;
using vl = vector<ll>;
using vvl = vector<vl>;
#define mp make_pair
#define pb push_back
#define _overload3(_1, _2, _3, name, ...) name
#define _rep(i, n) repi(i, 0, n)
#define repi(i, a, b) for (int i = int(a); i < int(b); i++)
#define rep(...) _overload3(__VA_ARGS__, repi, _rep, )(__VA_ARGS__)
#define rrep(i, n) for (int i = (n - 1); i >= 0; i--)
#define all(v) v.begin(), v.end()
#define sz(v) (int)((v).size())
#define MAX(v) *max_element(all(v))
#define MIN(v) *min_element(all(v))
#define Sort(v) sort(all(v))
#define Rev(v) reverse(all(v))
#define vec(type, name, ...) vector<type> name(__VA_ARGS__)
#define VEC(type, name, size)                                                  \
  vector<type> name(size);                                                     \
  in(name)
#define vv(type, name, h, ...)                                                 \
  vector<vector<type>> name(h, vector<type>(__VA_ARGS__))
#define VV(type, name, h, w)                                                   \
  vector<vector<type>> name(h, vector<type>(w));                               \
  in(name)
void debug_out() { cout << endl; }
template <typename Head, typename... Tail> void debug_out(Head H, Tail... T) {
  cout << H << " ";
  debug_out(T...);
}
#ifdef _DEBUG
#define debug(...) debug_out(__VA_ARGS__)
#else
#define debug(...)
#endif
template <typename T>
std::ostream &operator<<(std::ostream &os, std::vector<T> vec) {
  for (std::size_t i = 0; i < vec.size(); i++)
    os << vec[i] << (i + 1 == vec.size() ? "" : " ");
  return os;
}
inline void IN(void) { return; }
template <typename First, typename... Rest>
void IN(First &first, Rest &...rest) {
  cin >> first;
  IN(rest...);
  return;
}
template <class T> bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> bool chmin(T &a, const T &b) {
  if (b < a) {
    a = b;
    return 1;
  }
  return 0;
}
const ll INF = 1LL << 60;
const ll mod = 1000000007;
const int dx[8] = {1, 0, -1, 0, 1, 1, -1, -1};
const int dy[8] = {0, 1, 0, -1, 1, 1, -1, -1};

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  ll n, m, k;
  cin >> n >> m >> k;
  vector<ll> a(n), b(m);
  rep(i, n) cin >> a[i];
  rep(i, m) cin >> b[i];
  vector<ll> sa(n + 1), sb(m + 1);
  rep(i, n) sa[i + 1] = sa[i] + a[i];
  rep(i, m) sb[i + 1] = sb[i] + b[i];

  ll ans = 0;
  rep(i, n + 1) {
    if (sa[i] > k)
      continue;
    ll ok = 0, ng = m + 1;
    while (abs(ok - ng) > 1) {
      ll mid = (ok + ng) / 2;
      if (sa[i] + sb[mid] <= k)
        ok = mid;
      else
        ng = mid;
    }
    chmax(ans, i + ok);
  }
  cout << ans << endl;
}