Program for harmonic mean of numbers

Given an array of elements, find harmonic mean of numbers. 
Examples: 

Input : arr[] = {2.0, 1.0}
Output : 1.3333
Harmonic mean = 2/(1/2.0 + 1/1.0)
             = (2 * 2)/3
             = 1.333

Input : arr[] = {13.5, 14.5, 14.8, 15.2, 16.1}
Output : 14.7707

Harmonic mean is used when average of rates is required, below is the formula.
Harmonic mean of n numbers x₁, x₂, 
x₃, . . ., x_n can written as below.
Harmonic mean = n / ((1/x₁) + (1/x₂) + (1/x₃) + . . . + (1/x_n))

Below is the implementation of Harmonic Mean. 

C++

// CPP program to find harmonic mean of numbers.
#include <bits/stdc++.h>
using namespace std;

// Function that returns harmonic mean.
float harmonicMean(float arr[], int n)
{
    // Declare sum variables and initialize with zero.
    float sum = 0;
    for (int i = 0; i < n; i++)
        sum = sum + (float)1 / arr[i];
    return (float)n / sum;
}

// Driver code
int main()
{
    float arr[] = { 13.5, 14.5, 14.8, 15.2, 16.1 };
    int n = sizeof(arr) / sizeof(arr[0]);
    cout << harmonicMean(arr, n);
    return 0;
}

// This code is contributed by Aditya Kumar (adityakumar129)

C

// C program to find harmonic mean of numbers.
#include <stdio.h>

// Function that returns harmonic mean.
float harmonicMean(float arr[], int n)
{
    // Declare sum variables and initialize with zero.
    float sum = 0;
    for (int i = 0; i < n; i++)
        sum = sum + (float)1 / arr[i];
    return (float)n / sum;
}

// Driver code
int main()
{
    float arr[] = { 13.5, 14.5, 14.8, 15.2, 16.1 };
    int n = sizeof(arr) / sizeof(arr[0]);
    printf("%f",harmonicMean(arr, n));
    return 0;
}

// This code is contributed by Aditya Kumar (adityakumar129)

Java

// JAVA program to find harmonic mean of numbers.
import java.io.*;

class GFG {

    // Function that returns harmonic mean.
    static float harmonicMean(float arr[], int n)
    {
        // Declare sum variables and initialize with zero
        float sum = 0;
        for (int i = 0; i < n; i++)
            sum = sum + (float)1 / arr[i];
        return (float)n / sum;
    }

    // Driver code
    public static void main(String args[])
    {
        float arr[] = { 13.5f, 14.5f, 14.8f, 15.2f, 16.1f };
        int n = arr.length;
        System.out.println(harmonicMean(arr, n));
    }
}

// This code is contributed by Aditya Kumar (adityakumar129)

Python3

# Python 3 program to find harmonic
# mean of numbers.

# Function that returns harmonic mean.
def harmonicMean(arr, n) :

    # Declare sum variables and
    # initialize with zero.
    sm = 0
    for i in range(0, n) :
        sm = sm + (1) / arr[i];

    return n / sm


# Driver code
arr = [ 13.5, 14.5, 14.8, 15.2, 16.1 ];
n = len(arr)
print(harmonicMean(arr, n))

# This code is contributed by Nikita Tiwari.

C#

// C# program to find harmonic
// mean of numbers.
using System;

class GFG {

    // Function that returns harmonic mean.
    static float harmonicMean(float[] arr, int n)
    {
        // Declare sum variables and
        // initialize with zero
        float sum = 0;
        for (int i = 0; i < n; i++)
            sum = sum + (float)1 / arr[i];

        return (float)n / sum;
    }

    // Driver code
    public static void Main()
    {
        float[] arr = { 13.5f, 14.5f, 14.8f,
                        15.2f, 16.1f };
        int n = arr.Length;
        Console.WriteLine(harmonicMean(arr, n));
    }
}

/*This code is contributed by vt_m.*/

PHP

<?php
// PHP program to find
// harmonic mean of numbers.

// Function that returns
// harmonic mean.
function harmonicMean($arr, $n)
{

    // Declare sum variables and
    // initialize with zero
    $sum = 0;
    for ($i = 0; $i < $n; $i++)
        $sum = $sum + (float)
               (1 / $arr[$i]);

    return (float)($n / $sum);
}

// Driver code
$arr = array(13.5, 14.5, 14.8, 15.2, 16.1);
$n = sizeof($arr);
echo(harmonicMean($arr, $n));

// This code is contributed by Ajit.
?>

Javascript

<script>

// Javascript program to find harmonic mean of numbers.

// Function that returns harmonic mean.
function harmonicMean(arr, n)
{
    // Declare sum variables and initialize
    // with zero.
    let sum = 0;
    for (let i = 0; i < n; i++)
        sum = sum + (1 / arr[i]);

    return n/sum;
}

// Driver code

let arr = [ 13.5, 14.5, 14.8, 15.2, 16.1 ];
let n = arr.length;
document.write(harmonicMean(arr, n));

</script>

Output: 

14.7707

Time Complexity: O(n)

Auxiliary Space: O(1), since no extra space has been taken.
What if we are given elements and their frequencies?
If we are given n numbers and every number has some frequency then simply we use formula 
Harmonic mean = (Frequency-Sum) /((f₁/x₁) + (f₂/x₂) + (f₃/x₃) + . . . + (f_n/x_n)) 
Where f₁, f₂, f₃, . . ., f_n are the frequencies of elements and x₁, ₂, x₃, . . ., x_n are the elements of array.
Frequency-Sum = f₁ + f₂ + f₃, . . ., f_n
Examples: 

Input : num[] = {13, 14, 15, 16, 17}
        freq[] = {2, 5, 13, 7, 3}
Output : 15.0631

C++

// C++ program to find harmonic mean.
#include <bits/stdc++.h>
using namespace std;
// Function that returns harmonic mean.
float harmonicMean(int arr[], int freq[], int n)
{
    float sum = 0, frequency_sum = 0;
    for (int i = 0; i < n; i++) {
        sum = sum + (float)freq[i] / arr[i];
        frequency_sum  = frequency_sum  + freq[i];
    }
    return frequency_sum / sum;
}

// Driver code
int main()
{
    int num[] = { 13, 14, 15, 16, 17 };
    int freq[] = { 2, 5, 13, 7, 3 };
    int n = sizeof(num) / sizeof(num[0]);
    cout << harmonicMean(num, freq, n);
    return 0;
}

Java

// JAVA program to find harmonic mean.

class GFG {

    // Function that returns harmonic mean.
    static float harmonicMean(int arr[], int freq[],
                              int n)
    {
        float sum = 0, frequency_sum = 0;
        for (int i = 0; i < n; i++) {
            sum = sum + (float)freq[i] / arr[i];
            frequency_sum  = frequency_sum  + freq[i];
        }
        return (frequency_sum / sum);
    }

    // Driver code
    public static void main(String args[])
    {
        int num[] = { 13, 14, 15, 16, 17 };
        int freq[] = { 2, 5, 13, 7, 3 };
        int n = num.length;
        System.out.println(harmonicMean(num, freq, n));
    }
}

/*This code is contributed by Nikita Tiwari.*/

C#

// C# program to find harmonic mean.
using System;

class GFG {

    // Function that returns harmonic mean.
    static float harmonicMean(int[] arr, int[] freq,
                                              int n)
    {
        float sum = 0, frequency_sum = 0;
        for (int i = 0; i < n; i++) {
            sum = sum + (float)freq[i] / arr[i];
            frequency_sum = frequency_sum + freq[i];
        }
        return (frequency_sum / sum);
    }

    // Driver code
    public static void Main()
    {
        int[] num = { 13, 14, 15, 16, 17 };
        int[] freq = { 2, 5, 13, 7, 3 };
        int n = num.Length;
        Console.WriteLine(harmonicMean(num, freq, n));
    }
}

/*This code is contributed by vt_m.*/

PHP

<?php
// PHP program to find
// harmonic mean.

// Function that returns
// harmonic mean.
function harmonicMean($arr, $freq, $n)
{
    $sum = 0; $frequency_sum = 0;
    for ($i = 0; $i < $n; $i++)
    {
        $sum = $sum + (float)
               ($freq[$i] / $arr[$i]);
        $frequency_sum = $frequency_sum +
                                $freq[$i];
    }
    return ($frequency_sum / $sum);
}

// Driver code
$num = array(13, 14, 15, 16, 17);
$freq = array(2, 5, 13, 7, 3);
$n = sizeof($num);
echo(harmonicMean($num, $freq, $n));

// This code is contributed by Ajit.
?>

Javascript

<script>

// Javascript program to find harmonic mean.

// Function that returns harmonic mean.
function harmonicMean(arr, freq, n)
{
    let sum = 0, frequency_sum = 0;
    for (let i = 0; i < n; i++) {
        sum = sum + (freq[i] / arr[i]);
        frequency_sum  = frequency_sum  + freq[i];
    }
    return frequency_sum / sum;
}

// Driver code
let num = [ 13, 14, 15, 16, 17 ];
let freq = [ 2, 5, 13, 7, 3 ];
let n = num.length;
document.write(harmonicMean(num, freq, n));

</script>

Output: 

15.0631

Time Complexity: O(n)

Auxiliary Space: O(1)
Harmonic mean of numbers using harmonic_mean() in Python:
Simple Python program to find harmonic mean using harmonic_mean() function. 

Python3

#'harmonic_mean()' new function added in 'Python3.6' onwards.
#Program calculates Harmonic Mean using harmonic_mean()

#imports Python statistics library
import statistics
def harmonic_mean():
    list= [13.5, 14.5, 14.8, 15.2, 16.1]
    print(statistics.harmonic_mean(list))

#Driver code
harmonic_mean()


#This code is contributed by 'Abhishek Agrawal'.

Output: 14.770680729373778

Time Complexity: O(n)

Auxiliary Space: O(1)