字符串反转算法

<?php

$a = '123abc123abc';

$aLen   = strlen($a);

$revLen = floor($aLen / 2);

for ($i = 0; $i < $revLen; $i++) {
    $temp         = $a[$i];
    $a[$i]        = $a[$aLen - 1 - $i];
    $a[$aLen - 1] = $temp;

}

echo $a;  //cba321123abc