Reverse Integer
<p>Given a signed 32-bit integer <code>x</code>, return <code>x</code><em> with its digits reversed</em>. If reversing <code>x</code> causes the value to go outside the signed 32-bit integer range <code>[-2<sup>31</sup>, 2<sup>31</sup> - 1]</code>, then return <code>0</code>.</p>

<p><strong>Assume the environment does not allow you to store 64-bit integers (signed or unsigned).</strong></p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> x = 123
<strong>Output:</strong> 321
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> x = -123
<strong>Output:</strong> -321
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> x = 120
<strong>Output:</strong> 21
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>-2<sup>31</sup> &lt;= x &lt;= 2<sup>31</sup> - 1</code></li>
</ul>
Math
class Solution {
    /**
     * @param int $x
     * @return int
     */

    function reverse($x) {
        $isNegative = $x < 0;
        $x = abs($x);

        $reversed = 0;

        while ($x > 0) {
            $reversed = $reversed * 10 + ($x % 10);
            $x = (int) ($x / 10);
        }

        if ($isNegative) {
            $reversed *= -1;
        }
        if ($reversed < -pow(2, 31) || $reversed > pow(2, 31) - 1) {
            return 0;
        }

        return $reversed;
    }
}
