C++ solution for problem D

#include <cstring>
#include <map>
#include <deque>
#include <queue>
#include <stack>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <ctime>
#include <algorithm>
#include <vector>
#include <set>
#include <complex>
#include <list>
#include <climits>
#include <cctype>

using namespace std;

int n, m;

long long gen[50], lft[50], rght[50], tot[50];

int main() {
    scanf("%d%d", &n, &m);
    int len, num;
    for (int i = 0; i < n; i++) {
        scanf("%d", &len);
        int mx = -(1 << 30);
        int sum = 0;
        for (int j = 0; j < len; j++) {
            scanf("%d", &num);
            tot[i] += num;
            lft[i] = max(lft[i], tot[i]);
            rght[i] = min(rght[i], tot[i]);
            mx = max(mx, num);
            sum += num;
            if (sum < 0)
                sum = 0;
            else
                mx = max(mx, sum);
        }
        gen[i] = mx;
        rght[i] = tot[i] - rght[i];
    }
    long long cur = 0;
    long long best = (long long) (-1e18);
    while (m--) {
        int i;
        scanf("%d", &i);
        i--;
        best = max(best, gen[i]);
        if (cur)
            best = max(best, cur + lft[i]);
        cur = max(0ll, max(rght[i], cur + tot[i]));
    }
    cout << best << endl;
    return 0;
}