nth-digit

https://leetcode.com/problems/nth-digit/

public class Solution {
    public int findNthDigit(int n) {
        int k = 9;
        int b = 1;
        // 需要加上对b的限制
        while (b < 9 && n > k*b) {
            n -= k * b;
            k *= 10;
            b ++;
        }
        int rank = (n - 1) / b;
        int app = (n - 1) % b;
        int num = (int)Math.pow(10, b-1) + rank;
        for (int i=b-1; i>app; i--) {
            num /= 10;
        }
        return num % 10;
    }
}