CheckIfMatrixIsXMatrix.php

<?php

namespace App;

/**
 * Check if Matrix Is X-Matrix
 *
 * A square matrix is said to be an X-Matrix if both of the following conditions hold:
 *  - All the elements in the diagonals of the matrix are non-zero.
 *  - All other elements are 0.
 * Given a 2D integer array grid of size n x n representing a square matrix, return true if grid is an X-Matrix.
 * Otherwise, return false.
 *
 * Example 1:
 * Input: grid = [[2,0,0,1],[0,3,1,0],[0,5,2,0],[4,0,0,2]]
 * Output: true
 * Explanation: Refer to the diagram above.
 * An X-Matrix should have the green elements (diagonals) be non-zero and the red elements be 0.
 * Thus, grid is an X-Matrix.
 *
 * Example 2:
 * Input: grid = [[5,7,0],[0,3,1],[0,5,0]]
 * Output: false
 * Explanation: Refer to the diagram above.
 * An X-Matrix should have the green elements (diagonals) be non-zero and the red elements be 0.
 * Thus, grid is not an X-Matrix.
 *
 * https://leetcode.com/problems/check-if-matrix-is-x-matrix
 */
class CheckIfMatrixIsXMatrix
{
    /**
     * @param int[][] $grid
     * @return bool
     */
    public function checkXMatrix(array $grid): bool
    {
        for ($i = 0, $iMax = count($grid); $i < $iMax; $i++) {
            for ($j = 0, $jMax = count($grid); $j < $jMax; $j++) {
                if ($i === $j && $grid[$i][$j] === 0) {
                    return false;
                }

                if ($i + $j === count($grid) - 1 && $grid[$i][$j] === 0) {
                    return false;
                }

                if ($i !== $j && $grid[$i][$j] !== 0 && $i + $j !== count($grid) - 1) {
                    return false;
                }
            }
        }

        return true;
    }
}