Maximum sum

#include <iostream>
#include <vector>

using namespace std;

int main() {
    long long n;
    cin >> n;

    // Read the values
    vector<long long> v(n);
    for (long long i = 0; i < n; ++i)
        cin >> v[i];

    vector<long long> best(n, 0);
    vector<long long> acc(n, 0);

    // Find the first positive or the highest negative
    long long first = 0;
    long long highest_negative;
    while (v[first] < 0 and first < n)
    {
        if (first == 0)
            highest_negative = v[first];
        else if (v[first] > highest_negative)
            highest_negative = v[first];
        ++first;
    }

    // All negative numbers
    if (first == n)
        cout << highest_negative << endl;
    // Some positive number(s)
    else {
        long long max_count = v[first];
        long long partial_count = v[first];
        for (long long i = first+1; i < n; ++i)
        {
            partial_count += v[i];
            if (partial_count > max_count)
                max_count = partial_count;
            if(partial_count < 0)
                partial_count = 0;
        }

        cout << max_count << endl;
    }
}

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