Maximum sum

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef vector <ll> vl;
const ll inf = 1e18;

void out(const vl &a)
{
    for(auto x : a)
    {
        if(x == -inf)
            cerr << "i ";
        else
            cerr << x << " ";
    }
    cerr << "\n";
}

int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(0); cout.tie(0);

    ll n, i, ans;
    cin >> n;
    vl a(n), pre(n + 2, 0), pos(n + 2, -inf);
    for(i = 0; i < n; i++)
        cin >> a[i];
    for(i = 1; i <= n; i++)
        pre[i] = pre[i - 1] + a[i - 1];
    //out(pre);
    ans = a[0];
    pos[n] = pre[n];
    for(i = n - 1; i >= 0; i--)
        pos[i] = max(pos[i + 1], pre[i]);
    for(i = 1; i <= n; i++)
    {
        pre[i] = min(pre[i], pre[i - 1]);
        ans = max(ans, pos[i] - pre[i - 1]);
    }
    //out(pre); out(pos);
    cout << ans;
    return 0;
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED

Test 13

Verdict: ACCEPTED

Test 14

Verdict: ACCEPTED

Test 15

Verdict: ACCEPTED