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 01 0 1 1 11 1 1 1 11 0 0 1 0

在给定的二维字符数组，找出最大全为1的矩形包含的1的个数：

注意这里相当于求面积而已，只要求出边长就很好办了。边长用dp很好求，这题其实跟前面有道dp问题很像，以后有时间找出来，先贴下代码：

1 class Solution { 2 public: 3     int maximalSquare(vector
     
      
       >& matrix) { 4         if(!matrix.size()||!matrix[0].size()) return 0; 5         vector
       
        
         >dp(matrix.size(), vector
         
          (matrix[0].size(), 0)); 6         int maxVal = 0; 7         for(int i = 0; i < matrix.size(); ++i){ 8             if(matrix[i][0] == '1'){ 9                 dp[i][0] = 1;10                 maxVal = 1;11             }else dp[i][0] = 0;12         }13         for(int j = 0; j < matrix[0].size(); ++j){14             if(matrix[0][j] == '1'){15                 dp[0][j] = 1; 16                 maxVal = 1;17             }else dp[0][j] = 0;18         }19         for(int i = 1; i < matrix.size(); ++i){20             for(int j = 1; j < matrix[0].size(); ++j){21                 if(matrix[i][j] == '1'){22                     dp[i][j] = min(dp[i-1][j], min(dp[i][j-1], dp[i-1][j-1])) + 1;23                     maxVal = max(maxVal, dp[i][j]);24                 }else25                     dp[i][j] = 0;26             }27         }28         return maxVal*maxVal;29     }30 };