# Replace every elements in the array by its frequency in the array

Given an array of integers, replace every element by its frequency in the array.

Examples:

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

Input : arr[] = { 4 5 4 5 6 6 6 }
Output : 2 2 2 2 3 3 3
```

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

Approach:

1. Take a hash map, which will store the frequency of all the elements in the array.
2. Now, traverse once again.
3. Now, replace all the elements by its frequency.
4. Print the modified array.

## C++

 `// C++ program to replace the elements ` `// by their frequency in the array. ` `#include "iostream" ` `#include "unordered_map" ` `using` `namespace` `std; ` ` `  `void` `ReplaceElementsByFrequency(``int` `arr[], ``int` `n) ` `{ ` `    ``// Hash map which will store the ` `    ``// frequency of the elements of the array. ` `    ``unordered_map<``int``, ``int``> mp; ` ` `  `    ``for` `(``int` `i = 0; i < n; ++i) { ` ` `  `        ``// Increment the frequency ` `        ``// of the element by 1. ` `        ``mp[arr[i]]++; ` `    ``} ` ` `  `    ``// Replace every element by its frequency ` `    ``for` `(``int` `i = 0; i < n; ++i) { ` `        ``arr[i] = mp[arr[i]]; ` `    ``} ` `} ` ` `  `int` `main() ` `{ ` `    ``int` `arr[] = { 1, 2, 5, 2, 2, 5 }; ` `    ``int` `n = ``sizeof``(arr) / ``sizeof``(arr); ` ` `  `    ``ReplaceElementsByFrequency(arr, n); ` ` `  `    ``// Print the modified array. ` `    ``for` `(``int` `i = 0; i < n; ++i) { ` `        ``cout << arr[i] << ``" "``; ` `    ``} ` `    ``return` `0; ` `} `

## Java

 `import` `java.util.HashMap; ` ` `  `// Java program to replace the elements  ` `// by their frequency in the array. ` `class` `GFG { ` ` `  `    ``static` `void` `ReplaceElementsByFrequency(``int` `arr[], ``int` `n) { ` `        ``// Hash map which will store the  ` `        ``// frequency of the elements of the array.  ` `        ``HashMap mp = ``new` `HashMap(); ` ` `  `        ``for` `(``int` `i = ``0``; i < n; ++i) { ` ` `  `            ``// Increment the frequency  ` `            ``// of the element by 1.  ` `            ``if` `(mp.get(arr[i]) == ``null``) { ` `                ``mp.put(arr[i], ``1``); ` `            ``} ``else` `{ ` `                ``mp.put(arr[i], (mp.get(arr[i]) + ``1``)); ` `            ``} ` `            ``//mp[arr[i]]++;  ` `        ``} ` ` `  `        ``// Replace every element by its frequency  ` `        ``for` `(``int` `i = ``0``; i < n; ++i) { ` `            ``if` `(mp.get(arr[i]) != ``null``) { ` `                ``arr[i] = mp.get(arr[i]); ` `            ``} ` `            ``//arr[i] = mp[arr[i]];  ` `        ``} ` `    ``} ` ` `  `    ``public` `static` `void` `main(String[] args) { ` `        ``int` `arr[] = {``1``, ``2``, ``5``, ``2``, ``2``, ``5``}; ` `        ``int` `n = arr.length; ` ` `  `        ``ReplaceElementsByFrequency(arr, n); ` ` `  `        ``// Print the modified array.  ` `        ``for` `(``int` `i = ``0``; i < n; ++i) { ` `            ``System.out.print(arr[i] + ``" "``); ` `        ``} ` `    ``} ` `} ` `// This code contributed by 29AJayKumar `

## Python3

 `# Python 3 program to replace the elements ` `# by their frequency in the array. ` ` `  `def` `ReplaceElementsByFrequency(arr, n): ` `     `  `    ``# Hash map which will store the ` `    ``# frequency of the elements of the array. ` `    ``mp ``=` `{i:``0` `for` `i ``in` `range``(``len``(arr))} ` ` `  `    ``for` `i ``in` `range``(n): ` `         `  `        ``# Increment the frequency of the  ` `        ``# element by 1. ` `        ``mp[arr[i]] ``+``=` `1` ` `  `    ``# Replace every element by its frequency ` `    ``for` `i ``in` `range``(n): ` `        ``arr[i] ``=` `mp[arr[i]] ` ` `  `# Driver Code ` `if` `__name__ ``=``=` `'__main__'``: ` `    ``arr ``=` `[``1``, ``2``, ``5``, ``2``, ``2``, ``5``] ` `    ``n ``=` `len``(arr) ` ` `  `    ``ReplaceElementsByFrequency(arr, n); ` ` `  `    ``# Print the modified array. ` `    ``for` `i ``in` `range``(n): ` `        ``print``(arr[i], end ``=` `" "``) ` ` `  `# This code is contributed by ` `# Sahil_shelangia `

## C#

 `// C# program to replace the elements  ` `// by their frequency in the array. ` `using` `System; ` `using` `System.Collections.Generic;  ` `     `  `class` `GFG  ` `{ ` ` `  `    ``static` `void` `ReplaceElementsByFrequency(``int` `[]arr, ``int` `n)  ` `    ``{ ` `        ``// Hash map which will store the  ` `        ``// frequency of the elements of the array.  ` `        ``Dictionary<``int``,``int``> mp = ``new` `Dictionary<``int``,``int``>(); ` ` `  `        ``for` `(``int` `i = 0; i < n; ++i) ` `        ``{ ` ` `  `            ``// Increment the frequency  ` `            ``// of the element by 1.  ` `            ``if` `(!mp.ContainsKey(arr[i]))  ` `            ``{ ` `                ``mp.Add(arr[i], 1); ` `            ``}  ` `            ``else` `            ``{ ` `                ``var` `a = mp[arr[i]] + 1; ` `                ``mp.Remove(arr[i]); ` `                ``mp.Add(arr[i], a); ` `            ``} ` `        ``} ` ` `  `        ``// Replace every element by its frequency  ` `        ``for` `(``int` `i = 0; i < n; ++i)  ` `        ``{ ` `            ``if` `(mp[arr[i]] != 0)  ` `            ``{ ` `                ``arr[i] = mp[arr[i]]; ` `            ``} ` `            ``//arr[i] = mp[arr[i]];  ` `        ``} ` `    ``} ` ` `  `    ``// Driver code ` `    ``public` `static` `void` `Main(String[] args)  ` `    ``{ ` `        ``int` `[]arr = {1, 2, 5, 2, 2, 5}; ` `        ``int` `n = arr.Length; ` ` `  `        ``ReplaceElementsByFrequency(arr, n); ` ` `  `        ``// Print the modified array.  ` `        ``for` `(``int` `i = 0; i < n; ++i) ` `        ``{ ` `            ``Console.Write(arr[i] + ``" "``); ` `        ``} ` `    ``} ` `} ` ` `  `// This code contributed by Rajput-Ji `

Output :

```1 3 2 3 3 2
```

Time Complexity – O(N)

My Personal Notes arrow_drop_up Check out this Author's contributed articles.

If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.

Article Tags :
Practice Tags :

Be the First to upvote.

Please write to us at contribute@geeksforgeeks.org to report any issue with the above content.