1139. Largest 1-Bordered Square

Given a 2D grid of 0s and 1s, return the number of elements in the largest square subgrid that has all 1s on its border, or 0 if such a subgrid doesn't exist in the grid.

Example 1:

Input: grid = [[1,1,1],[1,0,1],[1,1,1]]
Output: 9

Example 2:

Input: grid = [[1,1,0,0]]
Output: 1

class Solution {
    public int largest1BorderedSquare(int[][] A) {
        int m = A.length, n = A[0].length;
        int[][] left = new int[m][n], top = new int[m][n];
        for (int i = 0; i < m; ++i) {
            for (int j = 0; j < n; ++j) {
                if (A[i][j] > 0) {
                    left[i][j] = j > 0 ? left[i][j - 1] + 1 : 1;
                    top[i][j] = i > 0 ? top[i - 1][j] + 1 : 1;
                }
            }
        }
        for (int k = Math.min(m, n); k > 0; --k) {
            for (int i = 0; i < m - k + 1; ++i) {
                for (int j = 0; j < n - k + 1; ++j) {
                    if (top[i + k - 1][j] >= k && top[i + k - 1][j + k - 1] >= k && left[i][j + k - 1] >= k
                            && left[i + k - 1][j + k - 1] >= k) {
                        return k * k;
                    }
                }
            }
        }
        return 0;
    }
}