Java: Print the number of prime numbers which are less than or equal to a given integer

Java Basic: Exercise-217 with Solution

Write a Java program to print the number of prime numbers less than or equal to a given integer.

Input:

n (1 ≤ n ≤ 999,999).

Pictorial Presentation:

Sample Solution-1:

Java Code:

 import java.util.Scanner;
public class Main {
 
    public static void main(String[] args) {
        System.out.println("Input the number(n):");
		Scanner s = new Scanner(System.in);
            int c = s.nextInt();
            int ans = check(c);
			System.out.println("Number of prime numbers which are less than or equal to n.:");
            System.out.println(ans);
       }
    static int check(int c) {
        boolean[] prime = new boolean[c+1];
        int count = 0;
        for(int i = 2; i <= Math.sqrt(c); i++) {
            for(int j = i + i; j <= c; j += i) {
                prime[j] = true;
            }
        }
        for(int i = 2; i <= c; i++) {
            if(!prime[i]) {
                count++;
            }
        }
        return count;
    }
}

Sample Output:

Input the number(n):
 1235
Number of prime numbers which are less than or equal to n.:
202

Flowchart:

Sample Solution-2:

Java Code:

import java.util.Scanner;
 public class test {
   public static void main(String[] args) {
     System.out.println("Input the number(n):");
     Scanner s = new Scanner(System.in);
     int c = s.nextInt();
     int prime_ctr = 0;
     for (int i = 2; i <= c; i++) {
       if (Check_Prime(i)) {
         prime_ctr++;
       }
     }
     System.out.println("Number of prime numbers which are less than or equal to " + c + ": " + prime_ctr);
   }
   public static boolean Check_Prime(int n) {
     for (int divisor = 2; divisor <= n / 2; divisor++) {
       if (n % divisor == 0) {
         return false;
       }
     }
     return true;
   }
 }

Sample Output:

Input the number(n):
 1235
Number of prime numbers which are less than or equal to 1235: 202

Flowchart:

Java Code Editor:

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