2319. Check if Matrix Is X-Matrix 

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class Solution {
    public boolean checkXMatrix(int[][] grid) {
        int n = grid.length;

        for (int i = 0; i < n; i++) {
            for (int j = 0; j < n; j++) {
                if (i == j || i + j == n - 1) {
                    // 对角线元素
                    if (grid[i][j] == 0) {
                        return false;
                    }
                } else {
                    // 非对角线元素
                    if (grid[i][j] != 0) {
                        return false;
                    }
                }
            }
        }

        return true;
    }
}

References

2319. Check if Matrix Is X-Matrix