Question

How to rearrange an array such that every second element becomes greater than its left and right element with PHP

Answer 1

function swap(&$arr, $i, $j) {
        $temp = $arr[$i];
        $arr[$i] = $arr[$j];
        $arr[$j] = $temp;
}
    
function rearrangeArray(&$arr) {
    $size = count($arr);
    
    for ($i = 1; $i < $size; $i += 2) {
        if ($arr[$i - 1] > $arr[$i]) {
            swap($arr, $i - 1, $i);
        }
        if ($i + 1 < $size && $arr[$i + 1] > $arr[$i]) {
            swap($arr, $i + 1, $i);
        }
    }
}
        
$arr = array(1, 3, 6, 5, 4, 2, 9, 8, 7);

rearrangeArray($arr);

print_r($arr);




/*
run:

Array
(
    [0] => 1
    [1] => 6
    [2] => 3
    [3] => 5
    [4] => 2
    [5] => 9
    [6] => 4
    [7] => 8
    [8] => 7
)

*/

 

70+ SQL courses for beginners and professionals