MaximalSquare.java

public class MaximalSquare {
    static int min(int a, int b, int c) {
        return Math.min(a, Math.min(b, c));
    }

    static int findMaxSquare(int[][] matrix) {
        int n = matrix.length;
        int m = matrix[0].length;
        int[][] memo = new int[n][m];
        int max = 0;
        // initialize
        // copy first column
        for (int i = 0; i < n; i++) {
            memo[i][0] = matrix[i][0];
            max = Math.max(max, memo[i][0]);
        }
        // copy first row
        for (int i = 1; i < m; i++) {
            memo[0][i] = matrix[0][i];
            max = Math.max(max, memo[0][i]);
        }
        // fill the rest
        for (int i = 1; i < n; i++) {
            for (int j = 1; j < m; j++) {
                if (matrix[i][j] == 1) {
                    memo[i][j] = min(memo[i - 1][j], memo[i - 1][j - 1], memo[i][j - 1]) + 1;
                } else {
                    memo[i][j] = 0;
                }
                max = Math.max(max, memo[i][j]);
            }
        }
        return max * max;
    }

    public static void main(String[] args) {
        int[][] matrix = {
                {1, 0, 1, 0, 0},
                {1, 0, 1, 1, 1},
                {1, 1, 1, 1, 1},
                {1, 0, 0, 1, 0}
        };
        System.out.println(findMaxSquare(matrix));
    }
}