Find the missing integer in an array if mean is given

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 + ..an)/N.
So (a1 + a2 + a3.. + X + ..aN) = Mean*N .
Missing element x = (Mean*N – (a1 + a2 + a3….aN))

C++

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// 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;
}

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Java

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// 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

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Python3

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# 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.

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C#

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// 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.

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PHP

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<?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
?>

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Output

The missing element : 30


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