[leedcode 221] 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.

public class Solution {
    public int maximalSquare(char[][] matrix) {
        //dp  dynamic programing.  以当前点(x,y) = ‘1‘ 为右下角的最大正方形的边长f(x,y) = min( f(x-1,y), f(x,y-1), f(x-1,y-1)) + 1.
        //之所以将dp声明为[row+1][col+1]，主要防止对第一排和第一列特殊进行讨论
        if(matrix==null||matrix.length<=0||matrix[0].length<=0) return 0;
        int row=matrix.length;
        int col=matrix[0].length;
        int res=0;
        int dp[][]=new int[row+1][col+1];
        for(int i=0;i<row;i++){
            for(int j=0;j<col;j++){
                if(matrix[i][j]==‘1‘){
                    dp[i+1][j+1]=Math.min(dp[i][j],Math.min(dp[i][j+1],dp[i+1][j]))+1;
                    res=Math.max(res,dp[i+1][j+1]);
                }

            }
        }
        return res*res;
    }
}