Dreptunghiul format doar din 0 de arie maxima

#include <bits/stdc++.h>

using namespace std;

ifstream fin("plaja.in");
ofstream fout("plaja.out");

const int NMAX = 1001;
int N, M, v[NMAX + 1], ans;
string s;

void max_self(int &a, int b) {
    a = max(a, b);
}

void checkSol(int x1, int x2, int y) {
    max_self(ans, (x2 - x1) * y);
}

void solve() {
    stack<int> S;
    for(int i = 1; i <= M + 1; ++i) {
        while(!S.empty() && v[S.top()] > v[i]) {
            int index = S.top();
            S.pop();
            if(S.empty())
                checkSol(0, min(i, M), v[index]);
            else
                checkSol(S.top(), i - 1, v[index]);
        }
        S.emplace(i);
    }
}

int main() {
    fin >> N >> M;
    for(int i = 0; i < N; ++i) {
        fin >> s;
        for(int j = 0; j < M; ++j)
            if(s[j] == '0')
                ++v[j + 1];
            else
                v[j + 1] = 0;
        solve();
    }
    fout << ans << '\n';
}