Nth number made of prime digits

Problem Statement - link #

Given a number ‘N’. The task is to find the Nth number whose each digit is a prime number i.e 2, 3, 5, 7. In other words you have to find nth number of this sequence : 2, 3, 5, 7, 22, 23 ,.. and so on.

Your Task: Complete primeDigits function and return the nth number of the given sequence made of prime digits.

Expected Time Complexity: O(|S|)
Expected Auxiliary Space: O(1)

Examples #

Example 1:

Input:
N = 10
Output: 33
Explanation:10th number in the sequence of
numbers whose each digit is prime is 33.

Example 2:

Input:
N = 21
Output: 222
Explanation:21st number in the sequence of
numbers whose each digit is prime is 222.

Constraints #

• 1 <= N <= 100

Solutions #

class Solution{
    public:
    //Function to find nth number made of only prime digits.
    int primeDigits(int n)
    {
        //code here
        string s = "2357";
        int count = 0;
        int num = 0;
        while( count <= n ){
            int temp = num;
            while(s.find(temp%10 + '0')!=-1) temp/=10;
            if(temp==0) count++;
            num++;
        }
        return --num;
    }
};