Maximal Square

问题描述

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. 

 

解决思路

动态规划。

 

程序

public class Solution {
    public int maximalSquare(char[][] matrix) {
        if (matrix == null || matrix.length == 0 || matrix[0].length == 0) {
			return 0;
		}

		int n = matrix.length, m = matrix[0].length;
		int[][] dp = new int[n][m];
		int max = 0;

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