221. Maximal Square

题目：

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.

链接： http://leetcode.com/problems/maximal-square/

7/19/2017

看答案做的

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

官方答案

https://leetcode.com/problems/maximal-square/#/solution

更多讨论

https://discuss.leetcode.com/category/229/maximal-square