Super Pow
<p>Your task is to calculate <code>a<sup>b</sup></code> mod <code>1337</code> where <code>a</code> is a positive integer and <code>b</code> is an extremely large positive integer given in the form of an array.</p>

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

<pre>
<strong>Input:</strong> a = 2, b = [3]
<strong>Output:</strong> 8
</pre>

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

<pre>
<strong>Input:</strong> a = 2, b = [1,0]
<strong>Output:</strong> 1024
</pre>

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

<pre>
<strong>Input:</strong> a = 1, b = [4,3,3,8,5,2]
<strong>Output:</strong> 1
</pre>

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

<ul>
	<li><code>1 &lt;= a &lt;= 2<sup>31</sup> - 1</code></li>
	<li><code>1 &lt;= b.length &lt;= 2000</code></li>
	<li><code>0 &lt;= b[i] &lt;= 9</code></li>
	<li><code>b</code> does not contain leading zeros.</li>
</ul>
Math; Divide and Conquer
func superPow(a int, b []int) int {
	const mod int = 1337
	ans := 1
	qpow := func(a, n int) int {
		ans := 1
		for ; n > 0; n >>= 1 {
			if n&1 == 1 {
				ans = ans * a % mod
			}
			a = a * a % mod
		}
		return ans
	}
	for i := len(b) - 1; i >= 0; i-- {
		ans = ans * qpow(a, b[i]) % mod
		a = qpow(a, 10)
	}
	return ans
}