dp[i][j] - 以 matrix[i][j] 为右下角的正方形的最大边长

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