TCS Coding Practice Question | Prime Numbers upto N

Given a number N, the task is to find the Prime Numbers from 1 to N using Command Line Arguments.

Examples:

Input: N = 7
Output: 2, 3, 5, 7

Input: N = 13
Output: 2, 3, 5, 7, 11, 13 

Approach:

• Since the number is entered as Command line Argument, there is no need for a dedicated input line
• Extract the input number from the command line argument
• This extracted number will be in String type.
• Convert this number into integer type and store it in a variable, say N
• Now loop through the numbers from 2 to N, using a variable say i, to check if they are prime or not. This is done as follows: 
  In each iteration, 
  • Check if any numbers from 2 to (i/2+1) divide i completely (i.e. if it is a factor of i).
  • If yes, then i is not a prime number. Hence check for next number
  • If no, then i is a prime number. Hence print the value of i and check for next number
• After the loop has ended, the prime numbers from 1 to N are printed on the screen.

Note: Please note that 1 is not checked in this scenarios because 1 is neither prime nor composite.

Program:

C

// C program to find
// the Prime Numbers from 1 to N
// using command line arguments

#include <stdio.h>

#include <stdlib.h> /* atoi */

// Function to check if x is prime
int isPrime(int x)
{
    int i;

    // Loop to check if x has any factor
    // other than 1 and x itself
    for (i = 2; i < x / 2 + 1; i++) {
        if (x % i == 0) {
            // Since i is a factor of x
            // x is not prime
            return 0;
        }
    }

    // x is prime
    return 1;
}

// Function to find prime numbers up to n
void findPrimes(int n)
{
    int i;

    // Loop from 2 to n
    // to find all prime numbers in between
    for (i = 2; i <= n; i++) {

        // Check if i is prime
        // If yes then print it
        // else continue to next number
        if (isPrime(i) == 1)
            printf("%d, ", i);
    }

    printf("\n");
}

// Driver code
int main(int argc, char* argv[])
{

    int n;

    // Check if the length of args array is 1
    if (argc == 1)
        printf("No command line arguments found.\n");
    else {

        // Get the command line argument and
        // Convert it from string type to integer type
        // using function "atoi( argument)"
        n = atoi(argv[1]);

        // Find all prime numbers upto n
        findPrimes(n);
    }
    return 0;
}

Java

// Java program to find
// the Prime Numbers from 1 to N
// using command line arguments

class GFG {

    // Function to check if x is prime
    public static int isPrime(int x)
    {
        int i;

        // Loop to check if x has any factor
        // other than 1 and x itself
        for (i = 2; i < x / 2 + 1; i++) {
            if (x % i == 0) {
                // Since i is a factor of x
                // x is not prime
                return 0;
            }
        }

        // x is prime
        return 1;
    }

    // Function to find prime numbers up to n
    public static void findPrimes(int n)
    {
        int i;

        // Loop from 2 to n
        // to find all prime numbers in between
        for (i = 2; i <= n; i++) {

            // Check if i is prime
            // If yes then print it
            // else continue to next number
            if (isPrime(i) == 1)
                System.out.print(i + ", ");
        }

        System.out.println();
    }

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

        // Check if length of args array is
        // greater than 0
        if (args.length > 0) {

            // Get the command line argument and
            // Convert it from string type to integer type
            int n = Integer.parseInt(args[0]);

            // Find all prime numbers upto n
            findPrimes(n);
        }
        else
            System.out.println("No command line "
                               + "arguments found.");
    }
}

Output:

• In C: 
  

• In Java: 
  

Time Complexity: O(N*N)
Auxiliary Space: O(1)