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 01 0 1 1 11 1 1 1 11 0 0 1 0Output: 4

 

用dp。二重循环，如果dp[i][j]=1，检查一下它的上、左、右，取三个值中的最小值+1 （dp[i][j]），再更新一下max。

注意dp的长度比matrix多1.

时间：O(N^2)，空间O(N^2)

class Solution {    public int maximalSquare(char[][] matrix) {        if(matrix == null || matrix.length == 0 || matrix[0].length == 0) return 0;                int m = matrix.length, n = matrix[0].length, max = 0;        int[][] dp = new int[m+1][n+1];                for(int i = 1; i <= m; i++) {            for(int j = 1; j <= n; j++) {                if(matrix[i-1][j-1] == '1') {                    dp[i][j] = Math.min(dp[i-1][j-1], Math.min(dp[i][j-1], dp[i-1][j])) + 1;                    max = Math.max(max, dp[i][j]);                }            }        }        return max * max;    }}