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
class Solution {
    public int findNthDigit(int n) {
        int k = 1, cnt = 9;
        while ((long) k * cnt < n) {
            n -= k * cnt;
            ++k;
            cnt *= 10;
        }
        int num = (int) Math.pow(10, k - 1) + (n - 1) / k;
        int idx = (n - 1) % k;
        return String.valueOf(num).charAt(idx) - '0';
    }
}