Pow(x, n)
<p>Implement <a href="http://www.cplusplus.com/reference/valarray/pow/" target="_blank">pow(x, n)</a>, which calculates <code>x</code> raised to the power <code>n</code> (i.e., <code>x<sup>n</sup></code>).</p>

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

<pre>
<strong>Input:</strong> x = 2.00000, n = 10
<strong>Output:</strong> 1024.00000
</pre>

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

<pre>
<strong>Input:</strong> x = 2.10000, n = 3
<strong>Output:</strong> 9.26100
</pre>

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

<pre>
<strong>Input:</strong> x = 2.00000, n = -2
<strong>Output:</strong> 0.25000
<strong>Explanation:</strong> 2<sup>-2</sup> = 1/2<sup>2</sup> = 1/4 = 0.25
</pre>

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

<ul>
	<li><code>-100.0 &lt; x &lt; 100.0</code></li>
	<li><code>-2<sup>31</sup> &lt;= n &lt;= 2<sup>31</sup>-1</code></li>
	<li><code>n</code> is an integer.</li>
	<li>Either <code>x</code> is not zero or <code>n &gt; 0</code>.</li>
	<li><code>-10<sup>4</sup> &lt;= x<sup>n</sup> &lt;= 10<sup>4</sup></code></li>
</ul>
Recursion; Math
/**
 * @param {number} x
 * @param {number} n
 * @return {number}
 */
var myPow = function (x, n) {
    const qpow = (a, n) => {
        let ans = 1;
        for (; n; n >>>= 1) {
            if (n & 1) {
                ans *= a;
            }
            a *= a;
        }
        return ans;
    };
    return n >= 0 ? qpow(x, n) : 1 / qpow(x, -n);
};
