# Sum of all even occurring element in an array

• Difficulty Level : Basic
• Last Updated : 30 Jul, 2021

Given an array of integers containing duplicate elements. The task is to find the sum of all even occurring elements in the given array. That is the sum of all such elements whose frequency is even in the array.

Examples

```Input : arr[] = {1, 1, 2, 2, 3, 3, 3}
Output : 6
The even occurring element are 1 and 2 (both occur two times).
Therefore sum of all 1's in the array = 1+1+2+2 = 6.

Input : arr[] = {10, 20, 30, 40, 40}
Output : 80
Element with even frequency are 40.
Sum = 40.```

Approach

• Traverse the array and use a unordered_map in C++ to store the frequency of elements of the array such that the key of map is the array element and value is its frequency in the array.
• Then, traverse the map to find the frequency of elements and check if it is even, if it is even, then add this element to sum.

Below is the implementation of the above approach:

## C++

 `// C++ program to find the sum of all even``// occurring elements in an array` `#include ``using` `namespace` `std;` `// Function to find the sum of all even``// occurring elements in an array``int` `findSum(``int` `arr[], ``int` `N)``{``    ``// Map to store frequency of elements``    ``// of the array``    ``unordered_map<``int``, ``int``> mp;` `    ``for` `(``int` `i = 0; i < N; i++) {``        ``mp[arr[i]]++;``    ``}` `    ``// variable to store sum of all``    ``// even occurring elements``    ``int` `sum = 0;` `    ``// loop to iterate through map``    ``for` `(``auto` `itr = mp.begin(); itr != mp.end(); itr++) {` `        ``// check if frequency is even``        ``if` `(itr->second % 2 == 0)``            ``sum += (itr->first) * (itr->second);``    ``}` `    ``return` `sum;``}` `// Driver Code``int` `main()``{``    ``int` `arr[] = { 10, 20, 20, 40, 40 };` `    ``int` `N = ``sizeof``(arr) / ``sizeof``(arr);` `    ``cout << findSum(arr, N);` `    ``return` `0;``}`

## Java

 `// Java program to find the sum of all even``// occurring elements in an array` `import` `java.util.HashMap;``import` `java.util.Iterator;``import` `java.util.Map;``import` `java.util.Map.Entry;` `public` `class` `GFG {``    ``public` `static` `int` `element(``int``[] arr, ``int` `n)``    ``{` `        ``Map map = ``new` `HashMap();``        ``for` `(``int` `i = ``0``; i < n; i++) {``            ``int` `count = ``0``;``            ``if` `(map.get(arr[i]) != ``null``) {``                ``count = map.get(arr[i]);``            ``}``            ``map.put(arr[i], count + ``1``);``        ``}` `        ``int` `sum = ``0``;``        ``for` `(Entry entry : map.entrySet()) {``            ``if` `(entry.getValue() % ``2` `== ``0``) {``                ``sum += entry.getKey() * entry.getValue();``            ``}``        ``}` `        ``return` `sum;``    ``}` `    ``public` `static` `void` `main(String[] args)``    ``{``        ``int` `arr[] = { ``1``, ``1``, ``2``, ``2``, ``3``, ``3``, ``3` `};` `        ``// sum should be = 1+1+2+2=6;``        ``int` `n = arr.length;``        ``System.out.println(element(arr, n));``    ``}``}`

## Python3

 `# Python3 program to find the sum``# of all even occurring elements``# in an array` `# Function to find the sum of all even``# occurring elements in an array``def` `findSum(arr, N):` `    ``# Map to store frequency of``    ``# elements of the array``    ``mp ``=` `{}` `    ``for` `i ``in` `range``(N):``        ``if` `arr[i] ``in` `mp:``            ``mp[arr[i]] ``+``=` `1``        ``else``:``            ``mp[arr[i]] ``=` `1` `    ``# Variable to store sum of all``    ``# even occurring elements``    ``Sum` `=` `0` `    ``# Loop to iterate through map``    ``for` `first, second ``in` `mp.items():` `        ``# Check if frequency is even``        ``if` `(second ``%` `2` `=``=` `0``):``            ``Sum` `+``=` `(first) ``*` `(second)` `    ``return` `Sum``    ` `# Driver code   ``arr ``=` `[ ``10``, ``20``, ``20``, ``40``, ``40` `]` `N ``=` `len``(arr)` `print``(findSum(arr, N))` `# This code is contributed by divyeshrabadiya07`

## C#

 `// C# program to find the sum of all even``// occurring elements in an array``using` `System;``using` `System.Collections.Generic;` `class` `GFG {``    ` `    ``static` `int` `element(``int``[] arr, ``int` `n)``    ``{``        ``Dictionary<``int``, ``int``> map = ``new` `Dictionary<``int``, ``int``>(); ``        ``for` `(``int` `i = 0; i < n; i++)``        ``{``            ` `            ``if``(!map.ContainsKey(arr[i]))``            ``{``                ``map.Add(arr[i], 1);``            ``}``            ``else``            ``{``                ``map[arr[i]] += 1;``            ``}``            ` `        ``}`` ` `        ``int` `sum = 0;``        ` `        ``foreach``(KeyValuePair<``int``, ``int``> entry ``in` `map)``        ``{``            ``if` `(entry.Value % 2 == 0)``            ``{``                ``sum += entry.Key * entry.Value;``            ``}``        ``}`` ` `        ``return` `sum;``    ``}``  ` `  ``// Driver code``  ``static` `void` `Main() {``        ``int``[] arr = { 10, 20, 20, 40, 40};`` ` `        ``int` `n = arr.Length;``        ``Console.WriteLine(element(arr, n));``  ``}``}` `// This code is contributed by divyesh072019`

## Javascript

 ``

Output:

`120`

Time Complexity: O(N), where N is the number of elements in the array.

#### Method 2:Using Built in python functions:

• Count the frequencies of every element using Counter function
• Traverse the frequency dictionary and sum all the elements with occurrence even frequency multiplied by its frequency.

Below is the implementation:

## Python3

 `# Python3 implementation``from` `collections ``import` `Counter`  `def` `sumEven(arr, n):` `    ``# Counting frequency of every``    ``# element using Counter``    ``freq ``=` `Counter(arr)``    ` `    ``# initializing sum 0``    ``sum` `=` `0``    ` `    ``# Traverse the freq and print all``    ``# sum all elements with even frequency``    ``# multiplied by its frequency``    ``for` `it ``in` `freq:``        ``if` `freq[it] ``%` `2` `=``=` `0``:``            ``sum` `=` `sum` `+` `it``*``freq[it]``    ``print``(``sum``)`  `# Driver code``arr ``=` `[``10``, ``20``, ``20``, ``40``, ``40``]``n ``=` `len``(arr)` `sumEven(arr, n)` `# This code is contributed by vikkycirus`

Output:

`120`

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