leetcode-----85. 最大矩形

• 链接：https://leetcode-cn.com/problems/maximal-rectangle/

代码

class Solution {
public:
    int largestRectangleArea(vector<int>& h) {
        int n = h.size();
        vector<int> left(n), right(n);
        stack<int> stk;

        for (int i = 0; i < n; ++i) {
            while (stk.size() && h[stk.top()] >= h[i]) stk.pop();
            if (stk.empty()) left[i] = -1;
            else left[i] = stk.top();
            stk.push(i);
        }
        stk = stack<int>();

        for (int i = n - 1; i >= 0; --i) {
            while (stk.size() && h[stk.top()] >= h[i]) stk.pop();
            if (stk.empty()) right[i] = n;
            else right[i] = stk.top();
            stk.push(i);
        }

        int ans = 0;
        for (int i = 0; i < n; ++i) ans = max(ans, h[i] * (right[i] - left[i] - 1));
        return ans;
    }

    int maximalRectangle(vector<vector<char>>& matrix) {
        if (matrix.empty() || matrix[0].empty()) return 0;
        int n = matrix.size(), m = matrix[0].size();
        vector<vector<int>> h(n, vector<int>(m));
        for (int i = 0; i < n; ++i) {
            for (int j = 0; j < m; ++j) {
                if (matrix[i][j] == '1') {
                    if (i) h[i][j] = 1 + h[i - 1][j];
                    else h[i][j] = 1;
                }
            }
        }    
        int ans = 0;
        for (int i = 0; i < n; ++i) ans = max(ans, largestRectangleArea(h[i]));
        return ans;
    }
};