1  /*
 2   * Write program to find Kth prime number
 3   */ 
 4  import java.util.Scanner;
 5  import java.util.ArrayList;
 6  
 7  public class assignment_22 {
 8      public static int kth_prime_no(int K) {
 9          int N = 1000;  // Upper bound for prime search
10          boolean[] array = new boolean[N + 1];  // Corrected boolean array declaration
11          
12          // Initialize the array
13          for (int i = 0; i <= N; i++) {
14              if (i == 0 || i == 1) {
15                  array[i] = false;  // 0 and 1 are not prime
16              } else {
17                  array[i] = true;  // Assume all others are prime initially
18              }
19          }
20  
21          // Sieve of Eratosthenes to mark non-prime numbers
22          for (int j = 2; j <= Math.sqrt(N); j++) {
23              if (array[j]) {  // If j is prime
24                  for (int k = j * j; k <= N; k += j) {  // Mark multiples as non-prime
25                      array[k] = false;
26                  }
27              }
28          }
29  
30          // Collect prime numbers in a list
31          ArrayList<Integer> primes = new ArrayList<>();
32          for (int i = 2; i <= N; i++) {
33              if (array[i]) {
34                  primes.add(i);
35              }
36          }
37  
38          // Return the K-th prime number
39          if (K - 1 < primes.size()) {
40              return primes.get(K - 1);  // ArrayList uses .get(index)
41          } else {
42              return -1;  // Return -1 if K is out of bounds
43          }
44      }
45  
46      public static void main(String[] args) {
47          Scanner sc = new Scanner(System.in);
48          System.out.print("Enter the value of K: ");
49          int k = sc.nextInt();
50          sc.close();
51  
52          int result = kth_prime_no(k);
53          if (result != -1) {
54              System.out.println("The " + k + "th prime number is: " + result);
55          } else {
56              System.out.println("Invalid input: K is too large.");
57          }
58      }
59  }