Nth Digit
<p>Given an integer <code>n</code>, return the <code>n<sup>th</sup></code> digit of the infinite integer sequence <code>[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, ...]</code>.</p>

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

<pre>
<strong>Input:</strong> n = 3
<strong>Output:</strong> 3
</pre>

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

<pre>
<strong>Input:</strong> n = 11
<strong>Output:</strong> 0
<strong>Explanation:</strong> The 11<sup>th</sup> digit of the sequence 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, ... is a 0, which is part of the number 10.
</pre>

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

<ul>
	<li><code>1 &lt;= n &lt;= 2<sup>31</sup> - 1</code></li>
</ul>
Math; Binary Search
func findNthDigit(n int) int {
	k, cnt := 1, 9
	for k*cnt < n {
		n -= k * cnt
		k++
		cnt *= 10
	}
	num := int(math.Pow10(k-1)) + (n-1)/k
	idx := (n - 1) % k
	return int(strconv.Itoa(num)[idx] - '0')
}