Maximal Rectangle [LeetCode]

Problem Description: Given a 2D binary matrix filled with 0's and 1's, find the largest rectangle containing all ones and return its area.

Basic idea: To increas one dimension by one, then calculate the maximum of other dimension every time.

 1 class Solution {

 2 public:

 3     int maximalRectangle(vector<vector<char> > &matrix) {

 4         // Note: The Solution object is instantiated only once and is reused by each test case.

 5         if(matrix.size() == 0 || matrix[0].size() == 0)

 6             return 0;

 7         int max_area = 0;

 8         int row = matrix.size();

 9         int column = matrix[0].size();

10         for(int i = 0; i < row; i ++) {

11             for( int j = 0; j < column; j ++) {

12                 if (matrix[i][j] == '0')

13                     continue;

14                 

15                 int tmp_area = 1;

16                 int max_row_idx = row - 1;

17                 int max_column_idx = j;

18                 while(max_column_idx < column){

19                     int l;

20                     for(l = i + 1; l <= max_row_idx; l ++){

21                          if (matrix[l][max_column_idx] == '0') 

22                             break;

23                     }

24                     max_row_idx = l - 1;

25                     tmp_area = (max_row_idx - i + 1) * (max_column_idx - j + 1);

26                     if(tmp_area > max_area)

27                         max_area = tmp_area;

28                     

29                     //increase column

30                     if ( matrix[i][max_column_idx + 1] == '1'){

31                         max_column_idx ++;

32                     }else{

33                         break;

34                     }

35                 }

36                 

37             }

38         }

39         return max_area;

40     }

41 };