Solution.cpp

class Solution {
public:
    int maximalRectangle(vector<vector<char>>& matrix) {
        int n = matrix[0].size();
        vector<int> heights(n);
        int ans = 0;
        for (auto& row : matrix) {
            for (int j = 0; j < n; ++j) {
                if (row[j] == '1')
                    ++heights[j];
                else
                    heights[j] = 0;
            }
            ans = max(ans, largestRectangleArea(heights));
        }
        return ans;
    }

    int largestRectangleArea(vector<int>& heights) {
        int res = 0, n = heights.size();
        stack<int> stk;
        vector<int> left(n, -1);
        vector<int> right(n, n);
        for (int i = 0; i < n; ++i) {
            while (!stk.empty() && heights[stk.top()] >= heights[i]) {
                right[stk.top()] = i;
                stk.pop();
            }
            if (!stk.empty()) left[i] = stk.top();
            stk.push(i);
        }
        for (int i = 0; i < n; ++i)
            res = max(res, heights[i] * (right[i] - left[i] - 1));
        return res;
    }
};