221. Maximal Square

DP

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
class Solution {
    public int maximalSquare(char[][] matrix) {
        int m = matrix.length, n = matrix[0].length;

        int[][] dp = new int[m][n];
        int maxSide = 0;

        for (int i = 0; i < m; i++) {
            for (int j = 0; j < n; j++) {
                if (matrix[i][j] == '1') {
                    if (i == 0 || j == 0) {
                        // 在边界线上的元素为 '1' 时，最大边长只能为 1
                        dp[i][j] = 1;
                    } else {
                        dp[i][j] = Math.min(dp[i - 1][j - 1], Math.min(dp[i][j - 1], dp[i - 1][j])) + 1;
                    }

                    maxSide = Math.max(maxSide, dp[i][j]);
                }
            }
        }

        return maxSide * maxSide;
    }
}

DP

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
class Solution {
    public int maximalSquare(char[][] matrix) {
        int m = matrix.length, n = matrix[0].length;

        int maxSquare = 0;
        int[][] dp = new int[m + 1][n + 1];

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

        return maxSquare;
    }
}

References

221. Maximal Square