How to find the nth prime number in Java

Question

Can someone help me with the code to find the nth prime number in Java? I am practicing for a coding competition and was stuck with this! I tried few things but those exceeded the time limit. So can someone help me with the problem?

Answer 1

Here is the code to find nth prime number.

import java.util.Scanner;
public class NthPrime {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    System.out.print("Enter n to compute the nth prime number: ");
    int nth = sc.nextInt(); 
    int num, count, i;
    num=1;
    count=0;
 
    while (count < nth){
      num=num+1;
      for (i = 2; i <= num; i++){ //Here we will loop from 2 to num
        if (num % i == 0) {
          break;
        }
      }
      if ( i == num){//if it is a prime number
        count = count+1;
      }
    }
    System.out.println("Value of nth prime: " + num);
  }
}

Output:

Enter n to compute the nth prime number: 5
Value of nth prime: 11

Hope this helps!!

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Comments

Can you please explain the logic??

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The logic is simple. First, you take input from the user asking the value of n. Then you run a loop finding all the prime numbers. Whenever a prime number is found, the count is increased and if the count is equal to the input of user (i.e., if the prime number found is the nth prime number), then print it.