w3resource

Java Exercises: 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 which are less than or equal to a given integer.

Input:

n (1 ≤ n ≤ 999,999).

Pictorial Presentation:

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

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:

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

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:

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

Java Code Editor:

Contribute your code and comments through Disqus.

Previous: Write a Java program which reads an integer n and find the number of combinations of a,b,c and d (0 ≤ a,b,c,d ≤ 9) where (a + b + c + d) will be equal to n.
Next: Write a Java program to compute the radius and the central coordinate (x, y) of a circle which is constructed by three given points on the plane surface.

What is the difficulty level of this exercise?

Test your Programming skills with w3resource's quiz.



Follow us on Facebook and Twitter for latest update.

Java: Tips of the Day

Java: Anagrams

Generates all anagrams of a string.

public static List<String> anagrams(String input) {
    if (input.length() <= 2) {
        return input.length() == 2
                ? Arrays.asList(input, input.substring(1) + input.substring(0, 1))
                : Collections.singletonList(input);
    }
    return IntStream.range(0, input.length())
            .mapToObj(i -> new SimpleEntry<>(i, input.substring(i, i + 1)))
            .flatMap(entry ->
                    anagrams(input.substring(0, entry.getKey()) + input.substring(entry.getKey() + 1))
                            .stream()
                            .map(s -> entry.getValue() + s))
            .collect(Collectors.toList());
}

Ref: https://bit.ly/3rvAdAK