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Check if a given array contains duplicate elements within k distance from each other
• Difficulty Level : Easy
• Last Updated : 31 Mar, 2021

Given an unsorted array that may contain duplicates. Also given a number k which is smaller than size of array. Write a function that returns true if array contains duplicates within k distance.
Examples:

```Input: k = 3, arr[] = {1, 2, 3, 4, 1, 2, 3, 4}
Output: false
All duplicates are more than k distance away.

Input: k = 3, arr[] = {1, 2, 3, 1, 4, 5}
Output: true
1 is repeated at distance 3.

Input: k = 3, arr[] = {1, 2, 3, 4, 5}
Output: false

Input: k = 3, arr[] = {1, 2, 3, 4, 4}
Output: true```

A Simple Solution is to run two loops. The outer loop picks every element ‘arr[i]’ as a starting element, the inner loop compares all elements which are within k distance of ‘arr[i]’. The time complexity of this solution is O(kn).
We can solve this problem in Θ(n) time using Hashing. The idea is to one by add elements to hash. We also remove elements which are at more than k distance from current element. Following is detailed algorithm.
1) Create an empty hashtable.
2) Traverse all elements from left from right. Let the current element be ‘arr[i]’
….a) If current element ‘arr[i]’ is present in hashtable, then return true.
….b) Else add arr[i] to hash and remove arr[i-k] from hash if i is greater than or equal to k

## C++

 `#include``using` `namespace` `std;` `/* C++ program to Check if a given array contains duplicate``   ``elements within k distance from each other */``bool` `checkDuplicatesWithinK(``int` `arr[], ``int` `n, ``int` `k)``{``    ``// Creates an empty hashset``    ``unordered_set<``int``> myset;` `    ``// Traverse the input array``    ``for` `(``int` `i = 0; i < n; i++)``    ``{``        ``// If already present n hash, then we found``        ``// a duplicate within k distance``        ``if` `(myset.find(arr[i]) != myset.end())``            ``return` `true``;` `        ``// Add this item to hashset``        ``myset.insert(arr[i]);` `        ``// Remove the k+1 distant item``        ``if` `(i >= k)``            ``myset.erase(arr[i-k]);``    ``}``    ``return` `false``;``}` `// Driver method to test above method``int` `main ()``{``    ``int` `arr[] = {10, 5, 3, 4, 3, 5, 6};``    ``int` `n = ``sizeof``(arr) / ``sizeof``(arr);``    ``if` `(checkDuplicatesWithinK(arr, n, 3))``        ``cout << ``"Yes"``;``    ``else``        ``cout << ``"No"``;``}` `//This article is contributed by Chhavi`

## Java

 `/* Java program to Check if a given array contains duplicate``   ``elements within k distance from each other */``import` `java.util.*;` `class` `Main``{``    ``static` `boolean` `checkDuplicatesWithinK(``int` `arr[], ``int` `k)``    ``{``        ``// Creates an empty hashset``        ``HashSet set = ``new` `HashSet<>();` `        ``// Traverse the input array``        ``for` `(``int` `i=``0``; i= k)``              ``set.remove(arr[i-k]);``        ``}``        ``return` `false``;``    ``}` `    ``// Driver method to test above method``    ``public` `static` `void` `main (String[] args)``    ``{``        ``int` `arr[] = {``10``, ``5``, ``3``, ``4``, ``3``, ``5``, ``6``};``        ``if` `(checkDuplicatesWithinK(arr, ``3``))``           ``System.out.println(``"Yes"``);``        ``else``           ``System.out.println(``"No"``);``    ``}``}`

## Python 3

 `# Python 3 program to Check if a given array``# contains duplicate elements within k distance``# from each other``def` `checkDuplicatesWithinK(arr, n, k):` `    ``# Creates an empty list``    ``myset ``=` `[]` `    ``# Traverse the input array``    ``for` `i ``in` `range``(n):``    ` `        ``# If already present n hash, then we``        ``# found a duplicate within k distance``        ``if` `arr[i] ``in` `myset:``            ``return` `True` `        ``# Add this item to hashset``        ``myset.append(arr[i])` `        ``# Remove the k+1 distant item``        ``if` `(i >``=` `k):``            ``myset.remove(arr[i ``-` `k])``    ``return` `False` `# Driver Code``if` `__name__ ``=``=` `"__main__"``:``    ` `    ``arr ``=` `[``10``, ``5``, ``3``, ``4``, ``3``, ``5``, ``6``]``    ``n ``=` `len``(arr)``    ``if` `(checkDuplicatesWithinK(arr, n, ``3``)):``        ``print``(``"Yes"``)``    ``else``:``        ``print``(``"No"``)` `# This code is contributed by ita_c`

## C#

 `/* C# program to Check if a given``array contains duplicate elements``within k distance from each other */``using` `System;``using` `System.Collections.Generic;` `class` `GFG``{``    ``static` `bool` `checkDuplicatesWithinK(``int` `[]arr, ``int` `k)``    ``{``        ``// Creates an empty hashset``        ``HashSet<``int``> ``set` `= ``new` `HashSet<``int``>();` `        ``// Traverse the input array``        ``for` `(``int` `i = 0; i < arr.Length; i++)``        ``{``            ``// If already present n hash, then we found``            ``// a duplicate within k distance``            ``if` `(``set``.Contains(arr[i]))``                ``return` `true``;` `            ``// Add this item to hashset``            ``set``.Add(arr[i]);` `            ``// Remove the k+1 distant item``            ``if` `(i >= k)``                ``set``.Remove(arr[i - k]);``        ``}``        ``return` `false``;``    ``}` `    ``// Driver code``    ``public` `static` `void` `Main (String[] args)``    ``{``        ``int` `[]arr = {10, 5, 3, 4, 3, 5, 6};``        ``if` `(checkDuplicatesWithinK(arr, 3))``            ``Console.WriteLine(``"Yes"``);``        ``else``            ``Console.WriteLine(``"No"``);``    ``}``}` `// This code has been contributed``// by 29AjayKumar`

## Javascript

 ``

Output:

`Yes`

This article is contributed by Anuj. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.

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