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.

 class Solution {
 public:
     int maximalSquare(vector<vector<char>>& matrix) {
         int n=matrix.size();
         if(n<) return ;
         int m=matrix[].size();
         if(m<) return ;
         vector<vector<int>> size(n,vector<int>(m,));
         int maxnum=;
         int i;
         for(i=;i<n;i++)
         {
             if(matrix[i][]=='')
             {
                 size[i][]=;
                 maxnum=;
             }
         }
         for(i=;i<m;i++)
         {
             if(matrix[][i]=='')
             {
                 size[][i]=;
                 maxnum=;
             }
         }

         int j;
         for(i=;i<n;i++)
         {
             for(j=;j<m;j++)
             {
                 if(matrix[i][j]=='')
                 {
                     size[i][j]=min(size[i-][j-],min(size[i-][j],size[i][j-]))+;
                     if(maxnum<size[i][j])
                        maxnum=size[i][j];
                 }
                 else
                     size[i][j]=;
             }
         }
         return maxnum*maxnum;
     }
 };