Write a java program to find average of prime locations.

Write a program to read an integer array and find the average of the numbers located on the Prime location(indexes).

• Round the average to two decimal places.
• Assume that the array starts with index 0.
• The return type (double) should be the average

Input and Output Format:

• Input consists of n+1 integers. The first integer corresponds to n, the number of elements in the array. The next ‘n’ integers correspond to the elements in the array.
• Output consists of a single Double value.

Note: Assume that the maximum number of elements in the array is 20.

Refer to sample output for formatting specifications

Sample Input 1:

8

4

1

7

6

5

8

6

9

Sample Output 1:

7.5

Find the average of prime locations in Java

• Input the size of an array. Create an array of size ‘n’.
• Add elements to an array. Pass them to display() method.
• Inside the method, declare and initialize variable count, sum, n1, count1,avg, and d to 0.
• Use nested for loop, start the outer loop index from 2 and check if the index is a prime number. If it is a prime number then increment the count value.
• If the count value is 2, then add the element at the i^th index to the sum variable.
• At last, calculate the average and use the decimal format to round the decimal places up to 2 digits.

import java.text.DecimalFormat;
import java.util.Scanner;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);

    int[] a = new int[20];
    int n = sc.nextInt();
    for (int i = 0; i < n; i++) {
      a[i] = sc.nextInt();
    }

    System.out.print(display(n, a));
  }

  public static double display(int n, int[] a) {
    int count = 0, sum = 0, n1 = 0, d = 0;
    int count1 = 0;
    double avg = 0;

    for (int i = 2; i < n; i++) {
      count = 0;
      for (int j = 1; j <= i; j++) {
        if (i % j == 0) {
          count++;
        }
      }
      if (count == 2) {
        sum = sum + a[i];
        count1++;
      }
    }
    avg = (double) (sum) / count1;
    DecimalFormat df = new DecimalFormat("#.00");
    double ddd = Double.parseDouble(df.format(avg));
    return ddd;
  }
}

Output

Java program to find the location of the Prime Number

Write a code to find the location of the given prime number in the series of Prime Numbers. Consider a number ‘N’ whose location we have to find. So, if we enter N = 5, then the location of the prime number would be 3.

Input and Output Format:

• Input consists of the number ‘N’.
• Output consists of locations

Refer to sample output for formatting specifications

Sample Input :

5[Prime Number]

Sample Output :

3[Location]

Following are the steps to find the prime locations:

• Input a prime number from the user.
• Create an array of locations and initialize the loc variable to 0.
• Using the for loop, we will get all the prime numbers along with their location.
• At last, just get the location of the element from an array.

package com.demo;

import java.text.DecimalFormat;
import java.util.Scanner;

public class Test {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();
        int locations[] = new int[1000];
        int loc = 0;
        for (int i = 2; i < 100; i++) {
            if (locations[i] == 0) {

                locations[i] = ++loc;
                for (int j = i * 2; j <= 100; j= j+i)
                    locations[j] = -1;
            }
        }
        System.out.println(locations[n]);
    }
}

Output

Thus, in this way, we learn how to find the average of all the prime locations. Along with finding the location of prime numbers.