LeetCode – Refresh – Maximal Rectangle

This is the extension of Largest Rectangle in Histogram. We can just project 2D matrix to 1D array and compute it line by line.

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