Find the missing integer in an array if mean is given

Last Updated : 20 Feb, 2023

Given an array of size N-1 and the mean of N elements (one element is not given). We need to find the missing value X in the array.

Examples:

Input : a[] = {2, 4, 20}, Mean = 9
Output : Missing Element = 10
Explanation : Mean of (2, 4, 20, 10) is (2 + 4 + 20 + 10)/4 = 9

Let x be the missing element
Mean = (a₁ + a₂ + a₃.. + X + ..a_n)/N. 
So (a₁ + a₂ + a₃.. + X + ..a_N) = Mean*N . 
Missing element x = (Mean*N - (a₁ + a₂ + a₃....a_N))

Implementation:

C++

// C++ program to find missing element in a
// given array from mean.
#include <bits/stdc++.h>
using namespace std;

// Size of a[] is N - 1 (one element missing)
int findMissing(int a[], int N, int mean)
{
  // Find sum of array elements
  int sum = 0; 
  for (int i = 0; i < N - 1; i++) 
    sum += a[i];  

  return (mean * N) - sum;
}

int main() {
  int a[] = {25, 65, 80};
  int mean = 50;
  int n = sizeof(a)/sizeof(a[0]);
  cout << "The missing element : " 
       << findMissing(a, n+1, mean)  << endl;
  return 0;
}

Java

// Java program to find missing element 
// in a given array from mean.
import java.io.*;

class GFG
{
    // Size of a[] is N - 1 (one element missing)
    public static int findMissing(int a[], int N, int mean)
    {
        // Find sum of array elements
        int sum = 0; 
        for (int i = 0; i < N - 1; i++) 
        sum += a[i]; 

        return (mean * N) - sum;
    }
    
    // Driver code
    public static void main (String[] args) 
    {
        int a[] = {25, 65, 80};
        int mean = 50;
        int n = a.length;
        System.out.println("The missing element : "
                           + findMissing(a, n + 1, mean));
        
    }
}

// This code is contributed by upendra bartwal

Python3

# Python3 code to find missing element
# in a given array from mean.

# Size of a[] is N - 1 
# (one element missing)
def findMissing( a , N , mean ):

    # Find sum of array elements
    sum = 0
    for i in range(N - 1):
        sum += a[i]
    
    return (mean * N) - sum

# Driver Code
a = [25, 65, 80]
mean = 50
n = len(a)
print("The missing element : ", end = '')
print(findMissing(a, n+1, mean))

# This code is contributed by Sharad Bhardwaj.

// C# program to find missing element
// in a given array from mean.
using System;

class GFG {
    
    // Size of a[] is N - 1
    // (one element missing)
    public static int findMissing(int[] a, int N, int mean)
    {
        
        // Find sum of array elements
        int sum = 0;
        for (int i = 0; i < N - 1; i++)
            sum += a[i];

        return (mean * N) - sum;
    }

    // Driver code
    public static void Main()
    {
        int[] a = { 25, 65, 80 };
        int mean = 50;
        int n = a.Length;
        Console.WriteLine("The missing element : "
                    + findMissing(a, n + 1, mean));
    }
}

// This code is contributed by vt_m.

PHP

<?php
// PHP program to find missing 
// element in a given array 
// from mean.

// Size of a[] is N - 1 
// (one element missing)
function findMissing($a, $N, $mean)
{
    
    // Find sum of array elements
    $sum = 0; 
    for ($i = 0; $i < $N - 1; $i++) 
        $sum += $a[$i]; 
    
    return ($mean * $N) - $sum;
}

// Driver Code
$a = array(25, 65, 80);
$mean = 50;
$n = count($a);
echo "The missing element : "
    .findMissing($a, $n + 1, $mean);
        
// This code is contributed by Sam007
?>

JavaScript

<script>

// Javascript program to find 
// missing element in a
// given array from mean.


// Size of a[] is N - 1 
// (one element missing)
function findMissing( a, N, mean)
{
// Find sum of array elements
let sum = 0;
for (let i = 0; i < N - 1; i++)
    sum += a[i];

return (mean * N) - sum;
}

    // Driver Code
    
    let a = [25, 65, 80];
    let mean = 50;
    let n = a.length;
    document.write("The missing element : "
        + findMissing(a, n+1, mean) + "</br>");
    
    
</script>

Output

The missing element : 30

Time complexity: O(N) where N is no of the elements in the given array.
Auxiliary space: O(1) since constant space is required.

Find the missing integer in an array if mean is given

Manish_100

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Find the missing integer in an array if mean is given

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