# Reduce the array such that each element appears at most 2 times

Given a sorted array arr of size N, the task is to reduce the array such that each element can appear at most two times.

Examples:

Input: arr[] = {1, 2, 2, 2, 3}
Output: {1, 2, 2, 3}
Explanation:
Remove 2 once, as it occurs more than 2 times.

Input: arr[] = {3, 3, 3}
Output: {3, 3}
Explanation:
Remove 3 once, as it occurs more than 2 times.

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

Approach: This can be solved with the help of two pointer algorithm.

1. Start travsering array from left and maintain two pointers.
2. One pointer (lets say i) is used to iterate the array.
3. And the second pointer (lets say st) moves forward to find the next unique element, the element at i appears more than twice.

Below is the implementation of the above approach:

## CPP

 `// C++ program to reduce the array ` `// such that each element appears ` `// at most 2 times ` ` `  `#include ` `using` `namespace` `std; ` ` `  `// Function to remove duplicates ` `void` `removeDuplicates(``int` `arr[], ``int` `n) ` `{ ` `    ``// Initalise 2nd pointer ` `    ``int` `st = 0; ` ` `  `    ``// Itereate over the array ` `    ``for` `(``int` `i = 0; i < n; i++) { ` ` `  `        ``if` `(i < n - 2 ` `            ``&& arr[i] == arr[i + 1] ` `            ``&& arr[i] == arr[i + 2]) ` `            ``continue``; ` ` `  `        ``// Updating the 2nd pointer ` `        ``else` `{ ` `            ``arr[st] = arr[i]; ` `            ``st++; ` `        ``} ` `    ``} ` ` `  `    ``cout << ``"{"``; ` `    ``for` `(``int` `i = 0; i < st; i++) { ` `        ``cout << arr[i]; ` ` `  `        ``if` `(i != st - 1) ` `            ``cout << ``", "``; ` `    ``} ` `    ``cout << ``"}"``; ` `} ` ` `  `// Driver code ` `int` `main() ` `{ ` `    ``int` `arr[] ` `        ``= { 1, 1, 1, 2, ` `            ``2, 2, 3, 3, ` `            ``3, 3, 3, 3, ` `            ``4, 5 }; ` ` `  `    ``int` `n = ``sizeof``(arr) ` `            ``/ ``sizeof``(arr); ` ` `  `    ``// Function call ` `    ``removeDuplicates(arr, n); ` ` `  `    ``return` `0; ` `} `

## Java

 `// Java program to reduce the array ` `// such that each element appears ` `// at most 2 times ` `class` `GFG ` `{ ` ` `  `// Function to remove duplicates ` `static` `void` `removeDuplicates(``int` `arr[], ``int` `n) ` `{ ` `    ``// Initalise 2nd pointer ` `    ``int` `st = ``0``; ` ` `  `    ``// Itereate over the array ` `    ``for` `(``int` `i = ``0``; i < n; i++) { ` ` `  `        ``if` `(i < n - ``2` `            ``&& arr[i] == arr[i + ``1``] ` `            ``&& arr[i] == arr[i + ``2``]) ` `            ``continue``; ` ` `  `        ``// Updating the 2nd pointer ` `        ``else` `{ ` `            ``arr[st] = arr[i]; ` `            ``st++; ` `        ``} ` `    ``} ` ` `  `    ``System.out.print(``"{"``); ` `    ``for` `(``int` `i = ``0``; i < st; i++) { ` `        ``System.out.print(arr[i]); ` ` `  `        ``if` `(i != st - ``1``) ` `            ``System.out.print(``", "``); ` `    ``} ` `    ``System.out.print(``"}"``); ` `} ` ` `  `// Driver code ` `public` `static` `void` `main(String[] args) ` `{ ` `    ``int` `arr[] = { ``1``, ``1``, ``1``, ``2``, ` `                  ``2``, ``2``, ``3``, ``3``, ` `                  ``3``, ``3``, ``3``, ``3``, ` `                  ``4``, ``5` `}; ` ` `  `    ``int` `n = arr.length; ` ` `  `    ``// Function call ` `    ``removeDuplicates(arr, n); ` `} ` `} ` ` `  `// This code is contributed by sapnasingh4991 `

## Python3

 `# Python3 program to reduce the array  ` `# such that each element appears  ` `# at most 2 times  ` ` `  `# Function to remove duplicates  ` `def` `removeDuplicates(arr, n) :  ` ` `  `    ``# Initalise 2nd pointer  ` `    ``st ``=` `0``;  ` ` `  `    ``# Itereate over the array  ` `    ``for` `i ``in` `range``(n) : ` ` `  `        ``if` `(i < n ``-` `2` `and` `arr[i] ``=``=` `arr[i ``+` `1``]  ` `            ``and` `arr[i] ``=``=` `arr[i ``+` `2``]) : ` `            ``continue``;  ` ` `  `        ``# Updating the 2nd pointer  ` `        ``else` `: ` `            ``arr[st] ``=` `arr[i];  ` `            ``st ``+``=` `1``;  ` ` `  `    ``print``(``"{"``,end``=``"")  ` `    ``for` `i ``in` `range``(st) : ` `        ``print``(arr[i],end``=``""); ` `         `  `        ``if` `(i !``=` `st ``-` `1``) : ` `            ``print``(``", "``,end``=``"");  ` `     `  `    ``print``(``"}"``,end``=``"");  ` ` `  `# Driver code  ` `if` `__name__ ``=``=` `"__main__"` `:  ` ` `  `    ``arr ``=` `[ ``1``, ``1``, ``1``, ``2``,  ` `            ``2``, ``2``, ``3``, ``3``,  ` `            ``3``, ``3``, ``3``, ``3``,  ` `            ``4``, ``5` `];  ` ` `  `    ``n ``=` `len``(arr); ` `     `  `    ``# Function call  ` `    ``removeDuplicates(arr, n);  ` ` `  `# This code is contributed by Yash_R `

## C#

 `// C# program to reduce the array ` `// such that each element appears ` `// at most 2 times ` `using` `System; ` ` `  `class` `GFG ` `{ ` `  `  `// Function to remove duplicates ` `static` `void` `removeDuplicates(``int` `[]arr, ``int` `n) ` `{ ` `    ``// Initalise 2nd pointer ` `    ``int` `st = 0; ` `  `  `    ``// Itereate over the array ` `    ``for` `(``int` `i = 0; i < n; i++) { ` `  `  `        ``if` `(i < n - 2 ` `            ``&& arr[i] == arr[i + 1] ` `            ``&& arr[i] == arr[i + 2]) ` `            ``continue``; ` `  `  `        ``// Updating the 2nd pointer ` `        ``else` `{ ` `            ``arr[st] = arr[i]; ` `            ``st++; ` `        ``} ` `    ``} ` `  `  `    ``Console.Write(``"{"``); ` `    ``for` `(``int` `i = 0; i < st; i++) { ` `        ``Console.Write(arr[i]); ` `  `  `        ``if` `(i != st - 1) ` `            ``Console.Write(``", "``); ` `    ``} ` `    ``Console.Write(``"}"``); ` `} ` `  `  `// Driver code ` `public` `static` `void` `Main(String[] args) ` `{ ` `    ``int` `[]arr = { 1, 1, 1, 2, ` `                  ``2, 2, 3, 3, ` `                  ``3, 3, 3, 3, ` `                  ``4, 5 }; ` `  `  `    ``int` `n = arr.Length; ` `  `  `    ``// Function call ` `    ``removeDuplicates(arr, n); ` `} ` `} ` ` `  `// This code is contributed by sapnasingh4991 `

Output:

```{1, 1, 2, 2, 3, 3, 4, 5}
```

Time complexity: O(N)
Space complexity: O(1)

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Improved By : sapnasingh4991, Yash_R