Check if the first and last digit of number N is prime and their sum is less than K

Given a number N, the task is to check if its first and last digit is a prime number and their sum is less than K, or not. If it is, then print Yes, else print No.
Examples:

Input: N = 322223, K = 10
Output: Yes

Input: N = 62531561, K = 15
Output: No

Approach:

• Check if the first and last digit of N is prime or not.
• If they are prime, then check if they are less than K or not
• If they are less than K as well, print Yes.
• In any other case, print No.

Below is the implementation of the above approach: 

C++

// C++ program to check
// if the first and last digit of number N
// is prime and their sum is less than K
#include <bits/stdc++.h>
using namespace std;

// Get the First digit of the number
int first(int n)
{
    int a = n;
    int c = 1;
    while (a != 0)
    {
        a /= 10;
        c = c * 10;
    }
    c = c / 10;
    int fi = n / c;
    return fi;
}

// Check if the digit is prime or not
bool prime(int n)
{
    switch (n)
    {
        case 2:
            return true;

        case 3:
            return true;

        case 5:
            return true;

        case 7:
            return true;

        default:
            return false;
    }
}

// Function to Check if the first
// and last digit of number N is prime
// and their sum is less than K
void check(int n, int k)
{

    // Last digit of the number
    int l = n % 10;

    // First digit of number
    int f = first(n);

    // Check if these are prime
    bool lp = prime(l);
    bool fp = prime(f);

    // If they are prime
    if (lp && fp)
    {

        // Check if they are less than k or not
        if (l + f < k)
            cout << "Yes\n";
        else
            cout << "No\n";
    }
    else
    {
        cout << "No\n";
    }
}

// Driver code
int main()
{
    // Test case 1
    int n = 322223;
    int k = 10;

    check(n, k);

    // Test case 2
    n = 62531561;
    k = 15;

    check(n, k);

    return 0;
}

// This code is contributed by PrinciRaj1992

Java

// Java program to check
// if the first and last digit of number N
// is prime and their sum is less than K

import java.lang.*;

public class crazy_number {

    // Get the First digit of the number
    public static int first(int n)
    {
        int a = n;
        int c = 1;
        while (a != 0) {
            a /= 10;
            c = c * 10;
        }
        c = c / 10;
        int fi = n / c;
        return fi;
    }

    // Check if the digit is prime or not
    public static boolean prime(int n)
    {

        switch (n) {
        case 2:
            return true;

        case 3:
            return true;

        case 5:
            return true;

        case 7:
            return true;

        default:
            return false;
        }
    }

    // Function to Check if the first
    // and last digit of number N is prime
    // and their sum is less than K
    public static void check(int n, int k)
    {

        // Last digit of the number
        int l = n % 10;

        // First digit of number
        int f = first(n);

        // Check if these are prime
        boolean lp = prime(l);
        boolean fp = prime(f);

        // If they are prime
        if (lp && fp) {

            // Check if they are less than k or not
            if (l + f < k)
                System.out.println("Yes");
            else
                System.out.println("No");
        }
        else {
            System.out.println("No");
        }
    }

    // Driver code
    public static void main(String args[])
    {

        // Test case 1
        int n = 322223;
        int k = 10;

        check(n, k);

        // Test case 2
        n = 62531561;
        k = 15;

        check(n, k);
    }
}

Python3

# Python3 program to check if
# the first and last digit of number N
# is prime and their sum is less than K

# Get the First digit of the number
def first(n):
    a = n
    c = 1
    while (a != 0):
        a //= 10
        c = c * 10

    c = c // 10
    fi = n // c
    return fi

# Check if the digit is prime or not
def prime(n):
    if n in [2, 3, 5, 7]:
        return True
    else:
        return False

# Function to Check if the first
# and last digit of number N is prime
# and their sum is less than K
def check(n, k):

    # Last digit of the number
    l = n % 10

    # First digit of number
    f = first(n)

    # Check if these are prime
    lp = prime(l)
    fp = prime(f)

    # If they are prime
    if (lp and fp):

        # Check if they are less than k or not
        if (l + f < k):
            print("Yes")
        else:
            print("No")
    else:
        print("No")

# Driver code

# Test case 1
n = 322223
k = 10

check(n, k)

# Test case 2
n = 62531561
k = 15

check(n, k)

# This code is contributed by Mohit kumar

C#

// C# program to check
// if the first and last digit of number N
// is prime and their sum is less than K
using System;

class GFG
{

    // Get the First digit of the number
    public static int first(int n)
    {
        int a = n;
        int c = 1;
        while (a != 0)
        {
            a /= 10;
            c = c * 10;
        }
        c = c / 10;
        int fi = n / c;
        return fi;
    }

    // Check if the digit is prime or not
    public static Boolean prime(int n)
    {
        switch (n)
        {
            case 2:
                return true;

            case 3:
                return true;

            case 5:
                return true;

            case 7:
                return true;

            default:
                return false;
        }
    }

    // Function to Check if the first
    // and last digit of number N is prime
    // and their sum is less than K
    public static void check(int n, int k)
    {

        // Last digit of the number
        int l = n % 10;

        // First digit of number
        int f = first(n);

        // Check if these are prime
        Boolean lp = prime(l);
        Boolean fp = prime(f);

        // If they are prime
        if (lp && fp)
        {

            // Check if they are less than k or not
            if (l + f < k)
                Console.WriteLine("Yes");
            else
                Console.WriteLine("No");
        }

        else
        {
            Console.WriteLine("No");
        }
    }

    // Driver code
    public static void Main(String []args)
    {

        // Test case 1
        int n = 322223;
        int k = 10;

        check(n, k);

        // Test case 2
        n = 62531561;
        k = 15;

        check(n, k);
    }
}

// This code is contributed by PrinciRaj1992

Javascript

<script>

      // JavaScript program to check
      // if the first and
      // last digit of number N
      // is prime and their sum
      // is less than K

      // Get the First digit
      // of the number
      function first(n) {
        var a = n;
        var c = 1;
        while (a != 0) {
          a = parseInt(a / 10);
          c = c * 10;
        }
        c = c / 10;
        var fi = parseInt(n / c);
        return fi;
      }

      // Check if the digit is
      // prime or not
      function prime(n) {
        switch (n) {
          case 2:
            return true;

          case 3:
            return true;

          case 5:
            return true;

          case 7:
            return true;

          default:
            return false;
        }
      }

      // Function to Check if the first
      // and last digit of number N is prime
      // and their sum is less than K
      function check(n, k) {
        // Last digit of the number
        var l = parseInt(n % 10);

        // First digit of number
        var f = first(n);

        // Check if these are prime
        var lp = prime(l);
        var fp = prime(f);

        // If they are prime
        if (lp && fp) {
          // Check if they are less
          // than k or not
          if (l + f < k)
          document.write("Yes <br>");
          else
          document.write("No <br>");
        } else {
          document.write("No <br>");
        }
      }

      // Driver code
      // Test case 1
      var n = 322223;
      var k = 10;

      check(n, k);

      // Test case 2
      n = 62531561;
      k = 15;

      check(n, k);

</script>

Output:

Yes
No

Time Complexity: O(log N)
Auxiliary Space: O(1), As constant extra space is used