400. Nth Digit

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Problem

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.

Code

class Solution {
    public int findNthDigit(int n) {
        int start = 1;
        int digitNum = 1;
        long base = 9;

        while(n > digitNum * base) {
            n -= digitNum * base;
            start *= 10;
            base *= 10;
            digitNum++;
        }

        start += (n - 1) / digitNum;

        String s = String.valueOf(start);
        char c = s.charAt((n - 1) % digitNum);

        return c - '0';
    }
}