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.

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/**
 * 1 - 9  : 9
 * 10 - 99 : 90
 * 100-999 : 900
 * ...
 */
public class Solution {
    public int findNthDigit(int n) {
        long count = 9;  // 因为要 9 ＊ 1000000000 注意会超出最大整数 ！！！！
        int len = 1;
        int start = 1;
        while(n > count * len){
            n -= count * len;
            count *= 10;
            len += 1;
            start *= 10;
        }
        start += (n -1) / len;
        String c = Integer.toString(start);
        return Character.getNumericValue(c.charAt((n-1) % len));
    }
}