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

nth-digit.java

class Solution {
    public int findNthDigit(int n) {
        long base = 1;
        int cnt = 1;// cnt -> number of digits
        
        while(n > 9 * base * cnt) {
            n -= (9 * base * cnt);
            cnt += 1;
            base *= 10;
        }
        long num = (n - 1) / cnt + base;
        String candidate = String.valueOf(num);
        return candidate.charAt((n - 1) % cnt) - '0';
    }
}