文章作者：Tyan
博客：noahsnail.com  |  CSDN  |  简书

1. Description

Nth Digit

2. Solution

• Version 1

class Solution {
public:
    int findNthDigit(int n) {
        int digits = 1;
        long base = 9;
        while(n > digits * base) {
            n -= digits * base;
            digits++;
            base *= 10;
        }
        int residual = n % digits;
        int quotient = n / digits;
        int target = base / 9 + quotient + (residual?1:0) - 1;
        if(residual == 0) {
            return target % 10;
        }
        char s = to_string(target)[residual - 1];
        return s - '0';
    }
};

• Version 2

class Solution {
public:
    int findNthDigit(int n) {
        int digits = 1;
        long base = 9;
        while(n > digits * base) {
            n -= digits * base;
            digits++;
            base *= 10;
        }
        int residual = n % digits;
        int quotient = n / digits;
        int target = base / 9 + quotient + (residual?1:0) - 1;
        int count = digits - residual + 1;
        if(residual == 0) {
            return target % 10;
        }
        int result = 0;
        while(count) {
            result = target % 10;
            target /= 10;
            count--;
        }
        return result;
    }
};

Reference

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