221 Maximal Square

https://leetcode.com/problems/maximal-square/description/

蛮有意思的题目，理解了解法不难做，但是初见很难想到吧

class Solution {
    public int maximalSquare(char[][] matrix) {
        int m = matrix.length;
        int n = matrix[0].length;
        // dp[i][j]是以i,j为右下角的正方形的最大边长
        int[][] dp = new int[m][n];
        int maxLen = 0;
        for (int i = 0; i < m; i++) {
            dp[i][0] = matrix[i][0] - '0';
            maxLen = Math.max(dp[i][0], maxLen);
        }
        for (int j = 0; j < n; j++) {
            dp[0][j] = matrix[0][j] - '0';
            maxLen = Math.max(dp[0][j], maxLen);
        }
        
        for (int i = 1; i < m; i++) {
            for (int j = 1; j < n; j++) {
                if (matrix[i][j] != '1') {
                    continue;
                }
                //画画图就清楚了，像拼七巧板
                dp[i][j] = Math.min(dp[i-1][j-1], Math.min(dp[i-1][j], dp[i][j-1]))+1;
                maxLen = Math.max(dp[i][j], maxLen);
            }
        }
        return maxLen*maxLen;
    }
}