LeetCode 400. 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.

分析:个位数:1-9,一共9个,共计9个数字;2位数:10-99,一共90个,共计180个数字; 3位数:100-999,一共900个,共计270个数字……以此类推,所以先算出它在几位数的区间,然后算出它是在这个区间内的第几个数,最后算出在这个数的第几位~