221. Maximal Square

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class Solution {
    public int maximalSquare(char[][] matrix) {
        int m = matrix.length;
        if (m == 0) return 0;
        int n = matrix[0].length;

        int[][] dp = new int[m + 1][n + 1];

        int max = 0;
        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 - 1][j], dp[i][j - 1])) + 1;
                    max = Math.max(max, dp[i][j]);
                }
            }
        }
        return max * max;
    }
}