<?php
function draw_pattern($rows, $cols) {
    for ($row = 0; $row < $rows; $row++) {
        for ($col = 0; $col < $cols; $col++) {
            if ($row % 2 === 0) {
                // $row * $cols + 1 gives you first number for that row
                // e.g. for row number 2 you get 2 * 4 + 1 = 9
                $num = $row * $cols + 1 + $col;
            } else {
                // ($row + 1) * $cols gives you last number for that row
                // e.g. for row number 1 you get (1 + 1) * 4 = 8
                $num = ($row + 1) * $cols - $col;
            }
            echo sprintf('%2d ', $num);
        }
        echo PHP_EOL;
    }
}
draw_pattern(3, 4);
echo PHP_EOL;
draw_pattern(4, 5);
echo PHP_EOL;
draw_pattern(5, 6);
 

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