Largest area of rectangle with permutations

• Time : $O(nmlogm)$
• Space : $O(m)$

int Solution::solve(vector<vector<int> > &A) {
    int n = A.size(), m = A[0].size(), res = 0;
    for(int i = 0; i < n; i++) {
        vector<int> now;
        for(int j = 0; j < m; j++) {
            if(i and A[i][j]) A[i][j] += A[i-1][j];
            if(A[i][j]) now.push_back(A[i][j]);
        }
        sort(rbegin(now), rend(now));
        for(int j = 0; j < now.size(); j++) res = max(res, (j + 1) * now[j]);
    }
    return res;
}