# 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}

**Approach:**

- Create a map and store the frequency of each element from the array to the same map.
- Then, traverse the array and find out which elements have odd frequencies with the help of the map.
- Ignore all those elements which have odd frequencies and print rest of them

Below is the implementation of the above approach:

## C++

`// C++ program to removes all odd` `// frequency elements from an Array` `#include <bits/stdc++.h>` `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[0]);` ` ` `// 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<Integer, Integer> mp = ` `new` `HashMap<Integer, Integer>();` ` ` `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` |

## Javascript

`<script>` `// Javascript program to removes all odd` `// frequency elements from an Array` ` ` `// Function that removes the` ` ` `// elements which have odd` ` ` `// frequencies in the array` ` ` `function` `remove(arr, n) {` ` ` `// Create a map to store the` ` ` `// frequency of each element` ` ` `let mp = ` `new` `Map();` ` ` `for` `(let i = 0; i < n; i++) {` ` ` `if` `(mp.has(arr[i])) {` ` ` `mp.set(arr[i], mp.get(arr[i]) + 1);` ` ` `} ` `else` `{` ` ` `mp.set(arr[i], 1);` ` ` `}` ` ` `}` ` ` ` ` `// Remove the elements which` ` ` `// have odd frequencies` ` ` `for` `(let i = 0; i < n; i++) {` ` ` ` ` `// If the element has` ` ` `// odd frequency then skip` ` ` `if` `((mp.has(arr[i]) && mp.get(arr[i]) % 2 == 1))` ` ` `continue` `;` ` ` ` ` `document.write(arr[i] + ` `", "` `);` ` ` `}` ` ` `}` ` ` `// Driver code` ` ` ` ` `let arr = [ 3, 3, 3, 2, 2, 4, 7, 7 ];` ` ` `let n = arr.length;` ` ` ` ` `// Function call` ` ` `remove(arr, n);` ` ` `</script>` |

**Output:**

2, 2, 7, 7,

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