Problem p03850 (C++)

Buggy submission (status: Runtime Error):
#include <algorithm>
#include <bitset>
#include <ciso646>
#include <cmath>
#include <complex>
#include <cstdio>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <unordered_map>
#include <utility>
#include <vector>
using namespace std;
typedef long long ll;
typedef unsigned int ui;
const ll mod = 1000000007;
const ll INF = (ll)1000000007 * 1000000007;
typedef pair<int, int> P;
#define stop                                                                   \
  char nyaa;                                                                   \
  cin >> nyaa;
#define rep(i, n) for (int i = 0; i < n; i++)
#define per(i, n) for (int i = n - 1; i >= 0; i--)
#define Rep(i, sta, n) for (int i = sta; i < n; i++)
#define rep1(i, n) for (int i = 1; i <= n; i++)
#define per1(i, n) for (int i = n; i >= 1; i--)
#define Rep1(i, sta, n) for (int i = sta; i <= n; i++)
typedef long double ld;
typedef complex<ld> Point;
const ld eps = 1e-4;
const ld pi = acos(-1.0);
typedef pair<ll, ll> LP;

int n;
bool m[1 << 18];
ll a[1 << 18];
ll s[1 << 18];
ll sx[1 << 18];
vector<int> v;
int main() {
  cin >> n;
  cin >> a[0];
  rep1(i, n - 1) {
    char t;
    cin >> t >> a[i];
    if (t == '-') {
      m[i] = true;
      v.push_back(i);
    }
  }
  rep(i, n) {
    s[i + 1] = s[i] + a[i];
    if (!m[i])
      sx[i + 1] = sx[i] + a[i];
    else
      sx[i + 1] = sx[i] - a[i];
  }
  ll ans = sx[n];
  rep(i, v.size() - 1) {
    int le = v[i], ri = v[i + 1];
    ll z = sx[le] - (s[ri] - s[le]) + s[n] - s[ri];
    ans = max(ans, z);
  }
  cout << ans << endl;
  // stop
  return 0;
}

Fixed submission:
#include <algorithm>
#include <bitset>
#include <ciso646>
#include <cmath>
#include <complex>
#include <cstdio>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <unordered_map>
#include <utility>
#include <vector>
using namespace std;
typedef long long ll;
typedef unsigned int ui;
const ll mod = 1000000007;
const ll INF = (ll)1000000007 * 1000000007;
typedef pair<int, int> P;
#define stop                                                                   \
  char nyaa;                                                                   \
  cin >> nyaa;
#define rep(i, n) for (int i = 0; i < n; i++)
#define per(i, n) for (int i = n - 1; i >= 0; i--)
#define Rep(i, sta, n) for (int i = sta; i < n; i++)
#define rep1(i, n) for (int i = 1; i <= n; i++)
#define per1(i, n) for (int i = n; i >= 1; i--)
#define Rep1(i, sta, n) for (int i = sta; i <= n; i++)
typedef long double ld;
typedef complex<ld> Point;
const ld eps = 1e-4;
const ld pi = acos(-1.0);
typedef pair<ll, ll> LP;

int n;
bool m[1 << 18];
ll a[1 << 18];
ll s[1 << 18];
ll sx[1 << 18];
vector<int> v;
int main() {
  cin >> n;
  cin >> a[0];
  rep1(i, n - 1) {
    char t;
    cin >> t >> a[i];
    if (t == '-') {
      m[i] = true;
      v.push_back(i);
    }
  }
  rep(i, n) {
    s[i + 1] = s[i] + a[i];
    if (!m[i])
      sx[i + 1] = sx[i] + a[i];
    else
      sx[i + 1] = sx[i] - a[i];
  }
  ll ans = sx[n];
  rep(i, (int)v.size() - 1) {
    int le = v[i], ri = v[i + 1];
    ll z = sx[le] - (s[ri] - s[le]) + s[n] - s[ri];
    ans = max(ans, z);
  }
  cout << ans << endl;
  // stop
  return 0;
}