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.

求出序列中第N个数字，比如N= 10，返回结果就为0，10拆分为1和0。

class Solution {
public:
    int findNthDigit(int n) {
        long long len = 1, cnt = 9, start = 1;
        while (n > len * cnt) {
            n -= len * cnt;
            ++len;
            cnt *= 10;
            start *= 10;
        }
        start += (n - 1) / len;
        string t = to_string(start);
        return t[(n - 1) % len] - '0';
    }
};