原题网址：https://leetcode.com/problems/nth-digit/
Find the nth digit of the infinite integer sequence 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, ...
Note: n is positive and will fit within the range of a 32-bit signed integer (n < 231).
Example 1:
Input: 3 Output: 3
Example 2:
Input: 11 Output: 0 Explanation: The 11th 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.方法：分析总结规律。
public class Solution { public int findNthDigit(int n) { if (n < 10) return n; long len = 1; long pow = 1; long count = 0; while (count + 9 * pow * len < n) { count += 9 * pow * len; pow *= 10; len++; } long base = pow; long offset = n - 1 - count; long num = base + offset / len; long remainder = offset % len; for(int i = 1; i < len - remainder; i++) { num /= 10; } return (int)(num % 10); } }