Leetcode: 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.

1-9 : count:9 * len:1

10-99： count:90 * len:2

100-999: count:900 * len:3

1000-9999: count: 9000 * len:4

maintain a count, len, start

 public class Solution {
     public int findNthDigit(int n) {
         int start = 1;
         int len = 1;
         long count = 9;
         while (n > len*count) {
             n -= len*count;
             start *= 10;
             len ++;
             count *= 10;
         }
         start += (n-1)/len;
         char res = Integer.toString(start).charAt((n-1)%len);
         return Character.getNumericValue(res);
     }
 }