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.

 1 class Solution {
 2 public:
 3     int maximalRectangle(vector<vector<char> > &matrix) {
 4         if (matrix.size() == 0) return 0;
 5         int n = matrix.size(), m = matrix[0].size(), result = 0;
 6         vector<int> height(m, 0), left(m), right(m);
 7         for (int i = 0; i < n; i++) {
 8             for (int j = 0; j < m; j++) {
 9                 if (matrix[i][j] == ‘1‘) height[j]++;
10                 else height[j] = 0;
11             }
12             for (int j = 0; j < m; j++) {
13                 left[j] = j;
14                 while (left[j] > 0 && height[j] <= height[left[j]-1]) left[j] = left[left[j]-1];
15             }
16             for (int j = m-1; j >= 0; j--) {
17                 right[j] = j;
18                 while (right[j] < m-1 && height[j] <= height[right[j]+1]) right[j] = right[right[j]+1];
19             }
20             for (int j = 0; j < m; j++) {
21                 result = max(result, height[j]*(right[j] - left[j] + 1));
22             }
23         }
24         return result;
25     }
26 };