# Delete all odd frequency elements from an Array

Given an array arr containing integers of size N, the task is to delete all the elements from the array that have odd frequencies.

Examples:

Input: arr[] = {3, 3, 3, 2, 2, 4, 7, 7}
Output: {2, 2, 7, 7}
Explanation:
Frequency of 3 = 3
Frequency of 2 = 2
Frequency of 4 = 1
Frequency of 7 = 2
Therefore, the elements 3 and 4 have odd frequencies, and hence the are removed.

Input: arr[] = {1, 3, 3, 1, 2, 5, 6, 5}
Output: {1, 3, 3, 1, 5, 5}

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Approach:

Below is the implementation of the above approach:

## C++

 `// C++ program to removes all odd ` `// frequency elements from an Array ` ` `  `#include ` `using` `namespace` `std; ` ` `  `// Function that removes the ` `// elements which have odd ` `// frequencies in the array ` `void` `remove``(``int` `arr[], ``int` `n) ` `{ ` `    ``// Create a map to store the ` `    ``// frequency of each element ` `    ``unordered_map<``int``, ``int``> m; ` `    ``for` `(``int` `i = 0; i < n; i++) { ` `        ``m[arr[i]]++; ` `    ``} ` ` `  `    ``// Remove the elements which ` `    ``// have odd frequencies ` `    ``for` `(``int` `i = 0; i < n; i++) { ` ` `  `        ``// If the element has ` `        ``// odd frequency then skip ` `        ``if` `((m[arr[i]] & 1)) ` `            ``continue``; ` ` `  `        ``cout << arr[i] << ``", "``; ` `    ``} ` `} ` ` `  `// Driver code ` `int` `main() ` `{ ` `    ``int` `arr[] ` `        ``= { 3, 3, 3, 2, ` `            ``2, 4, 7, 7 }; ` `    ``int` `n = ``sizeof``(arr) / ``sizeof``(arr); ` ` `  `    ``// Function call ` `    ``remove``(arr, n); ` ` `  `    ``return` `0; ` `} `

## Java

 `// Java program to removes all odd ` `// frequency elements from an Array ` `import` `java.util.*; ` ` `  `class` `GFG { ` ` `  `    ``// Function that removes the ` `    ``// elements which have odd ` `    ``// frequencies in the array ` `    ``static` `void` `remove(``int` `arr[], ``int` `n) { ` `        ``// Create a map to store the ` `        ``// frequency of each element ` `        ``HashMap mp = ``new` `HashMap(); ` `        ``for` `(``int` `i = ``0``; i < n; i++) { ` `            ``if` `(mp.containsKey(arr[i])) { ` `                ``mp.put(arr[i], mp.get(arr[i]) + ``1``); ` `            ``} ``else` `{ ` `                ``mp.put(arr[i], ``1``); ` `            ``} ` `        ``} ` ` `  `        ``// Remove the elements which ` `        ``// have odd frequencies ` `        ``for` `(``int` `i = ``0``; i < n; i++) { ` ` `  `            ``// If the element has ` `            ``// odd frequency then skip ` `            ``if` `((mp.containsKey(arr[i]) && mp.get(arr[i]) % ``2` `== ``1``)) ` `                ``continue``; ` ` `  `            ``System.out.print(arr[i] + ``", "``); ` `        ``} ` `    ``} ` ` `  `    ``// Driver code ` `    ``public` `static` `void` `main(String[] args) { ` `        ``int` `arr[] = { ``3``, ``3``, ``3``, ``2``, ``2``, ``4``, ``7``, ``7` `}; ` `        ``int` `n = arr.length; ` ` `  `        ``// Function call ` `        ``remove(arr, n); ` ` `  `    ``} ` `} ` ` `  `// This code is contributed by Rajput-Ji `

## Python3

 `# Python3 program to removes all odd  ` `# frequency elements from an Array  ` ` `  `# Function that removes the  ` `# elements which have odd  ` `# frequencies in the array  ` `def` `remove(arr,  n) : ` ` `  `    ``# Create a map to store the ` `    ``# frequency of each element ` `    ``m ``=` `dict``.fromkeys(arr,``0``); ` `    ``for` `i ``in` `range``(n) : ` `        ``m[arr[i]] ``+``=` `1``; ` `         `  `    ``# Remove the elements which ` `    ``# have odd frequencies ` `    ``for` `i ``in` `range``(n) : ` ` `  `        ``# If the element has  ` `        ``# odd frequency then skip ` `        ``if` `((m[arr[i]] & ``1``)) : ` `            ``continue``; ` `             `  `        ``print``(arr[i],end``=` `", "``);  ` ` `  `# Driver code  ` `if` `__name__ ``=``=` `"__main__"` `: ` ` `  `    ``arr    ``=` `[ ``3``, ``3``, ``3``, ``2``,  ` `            ``2``, ``4``, ``7``, ``7` `];  ` `    ``n ``=` `len``(arr);  ` ` `  `    ``# Function call  ` `    ``remove(arr, n);  ` ` `  `# This code is contributed by Yash_R `

## C#

 `// C# program to removes all odd ` `// frequency elements from an Array ` `using` `System; ` `using` `System.Collections.Generic; ` ` `  `class` `GFG { ` `  `  `    ``// Function that removes the ` `    ``// elements which have odd ` `    ``// frequencies in the array ` `    ``static` `void` `remove(``int` `[]arr, ``int` `n) { ` ` `  `        ``// Create a map to store the ` `        ``// frequency of each element ` `        ``Dictionary<``int``, ``int``> mp = ``new` `Dictionary<``int``, ``int``>(); ` `        ``for` `(``int` `i = 0; i < n; i++) { ` `            ``if` `(mp.ContainsKey(arr[i])) { ` `                ``mp[arr[i]] =  mp[arr[i]] + 1; ` `            ``} ``else` `{ ` `                ``mp.Add(arr[i], 1); ` `            ``} ` `        ``} ` `  `  `        ``// Remove the elements which ` `        ``// have odd frequencies ` `        ``for` `(``int` `i = 0; i < n; i++) { ` `  `  `            ``// If the element has ` `            ``// odd frequency then skip ` `            ``if` `((mp.ContainsKey(arr[i]) && mp[arr[i]] % 2 == 1)) ` `                ``continue``; ` `  `  `            ``Console.Write(arr[i] + ``", "``); ` `        ``} ` `    ``} ` `  `  `    ``// Driver code ` `    ``public` `static` `void` `Main(String[] args) { ` `        ``int` `[]arr = { 3, 3, 3, 2, 2, 4, 7, 7 }; ` `        ``int` `n = arr.Length; ` `  `  `        ``// Function call ` `        ``remove(arr, n); ` `    ``} ` `} ` ` `  `// This code is contributed by 29AjayKumar `

Output:

```2, 2, 7, 7,
```

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Improved By : Rajput-Ji, Yash_R, 29AjayKumar