second-hole.php

<?php

function transpose($matrix) {
    $transposed = [];
    $numberOfColumns = count($matrix[0]);
    $numberOfRows = count($matrix);
    for ($column = 0; $column < $numberOfColumns; $column++) {
        $transposed[$column] = [];
        for ($row = 0; $row < $numberOfRows; $row++) {
            $transposed[$column][] = $matrix[$row][$column];
        }
    }
    return $transposed;
}