Nth Digit in C++



Suppose we have one infinite integer sequence, we have to find the nth digit of this sequence. So if the input is 11, then the output will be 0 as if we place the numbers like 123456789101112, so the 11th digit is 0.

To solve this, we will follow these steps −

  • len := 0 and cnt := 9 and start := 1

  • while n > len * cnt

    • n := n – (len * cnt)

    • cnt := cnt * 10, start := start * 10

    • increase len by 1

  • start := start +(n - 1) / len

  • s := start as string

  • return s[(n – 1) mod len]

Example (C++)

Let us see the following implementation to get a better understanding −

 Live Demo

#include <bits/stdc++.h>
using namespace std;
typedef long long int lli;
class Solution {
public:
   int findNthDigit(int n) {
      lli len = 1;
      lli cnt = 9;
      lli start = 1;
      while(n > len * cnt){
         n -= len * cnt;
         cnt *= 10;
         start *= 10;
         len++;
      }
      start += (n - 1) / len;
      string s = to_string(start);
      return s[(n - 1) % len] - '0';
   }
};
main(){
   Solution ob;
   cout << (ob.findNthDigit(11));
}

Input

11

Output

0

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