Maximal Square

Given a 2D binary matrix filled with 0's and 1's, find the largest square containing all 1's and return its area.

For example, given the following matrix:

1 0 1 0 0

1 0 1 1 1

1 1 1 1 1

1 0 0 1 0

Return 4.

 1 class Solution {

 2 public:

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

 4         int n=matrix.size();

 5         if(n<1) return 0;

 6         int m=matrix[0].size();

 7         if(m<1) return 0;

 8         vector<vector<int>> size(n,vector<int>(m,0));

 9         int maxnum=0;

10         int i;

11         for(i=0;i<n;i++)

12         {

13             if(matrix[i][0]=='1')

14             {

15                 size[i][0]=1;

16                 maxnum=1;

17             }

18         }

19         for(i=0;i<m;i++)

20         {

21             if(matrix[0][i]=='1')

22             {

23                 size[0][i]=1;

24                 maxnum=1;

25             }

26         }

27         

28         int j;

29         for(i=1;i<n;i++)

30         {

31             for(j=1;j<m;j++)

32             {

33                 if(matrix[i][j]=='1')

34                 {

35                     size[i][j]=min(size[i-1][j-1],min(size[i-1][j],size[i][j-1]))+1;

36                     if(maxnum<size[i][j])

37                        maxnum=size[i][j];

38                 }

39                 else

40                     size[i][j]=0;

41             }

42         }

43         return maxnum*maxnum;

44     }

45 };