leetcode

Given a 2D binary matrix filled with 0’s and 1’s, find the largest rectangle containing only 1’s and return its area.

Example:

Input:
[
[“1”,“0”,“1”,“0”,“0”],
[“1”,“0”,“1”,“1”,“1”],
[“1”,“1”,“1”,“1”,“1”],
[“1”,“0”,“0”,“1”,“0”]
]
Output: 6

class Solution {
public:
    int maximalRectangle(vector<vector<char>> &matrix) {
        if (matrix.size() == 0)
            return 0;
        int n = matrix.size(), m = matrix[0].size(), sum = 0;
        vector<int> height(m, 0), right(m, m), left(m, 0);
        for (int i = 0; i < n; i++) {
            int cur_left = 0, cur_right = m;
            for (int j = 0; j < m; j++) {
                if (matrix[i][j] == '1')
                    height[j]++;
                else
                    height[j] = 0;
            }
            for (int j = 0; j < m; j++) {
                if (matrix[i][j] == '1') {
                    left[j] = max(left[j], cur_left);
                } else {
                    left[j] = 0, cur_left = j + 1;
                }
            }
            for (int j = m - 1; j >= 0; --j) {
                if (matrix[i][j] == '1') {
                    right[j] = min(right[j], cur_right);
                } else {
                    right[j] = m, cur_right = j;
                }
            }
            for (int j = 0; j < m; j++) {
                sum = max(sum, (right[j] - left[j]) * height[j]);
            }
        }
        return sum;
    }
};