[Leetcode221]最大面积 Maximal Square

【题目】

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

Example:

Input: 

1 0 1 0 0
1 0 1 1 1
1 1 1 1 1
1 0 0 1 0

Output: 4

【思路】

1. dp square面积和三个有关
2. 注意特殊空集条件

【代码】

class Solution {
    public int maximalSquare(char[][] matrix) {
        if(matrix.length==0)
            return 0;
        int dp[][]=new int[matrix.length+1][matrix[0].length+1];
        int ans=0;

        for(int i=1;i<matrix.length+1;i++){
            for(int j=1;j<matrix[0].length+1;j++){
                if(matrix[i-1][j-1]=='1'){
                    dp[i][j]=Math.min(Math.min(dp[i-1][j],dp[i][j-1]),dp[i-1][j-1])+1;
                    ans=Math.max(ans,dp[i][j]);
                }
            }
        }
        return ans*ans;
    }
}