Skip to content
Related Articles
Minimum array element changes to make its elements 1 to N
• Difficulty Level : Medium
• Last Updated : 06 May, 2021

Suppose you are given an array with N elements with any integer values. You need to find the minimum number of elements of the array which must be changed so that array has all integer values between 1 and N(including 1, N).
Examples:

```Input : arr[] = {1 4 5 3 7}
Output : 1
We need to replace 7 with 2 to satisfy
condition hence minimum changes is 1.

Input : arr[] = {8 55 22 1 3 22 4 5}
Output :3```

We insert all elements in a hash table. We then iterate from 1 to N and check whether the element is present in the hash table. If it is not present than increment count. The final value of count will be the minimum changes required.

## C++

 `// Count minimum changes to make array``// from 1 to n``#include ``using` `namespace` `std;` `int` `countChanges(``int` `arr[], ``int` `n)``{``    ``// it will contain all initial elements``    ``// of array for log(n) complexity searching``    ``unordered_set<``int``> s;` `    ``// Inserting all elements in a hash table``    ``for` `(``int` `i = 0; i < n; i++)``        ``s.insert(arr[i]);``    ` `    ``// Finding elements to be changed``    ``int` `count = 0;``    ``for` `(``int` `i = 1; i <= n; i++)``        ``if` `(s.find(i) == s.end())``            ``count++;` `    ``return` `count;``}` `int` `main()``{``    ``int` `arr[] = {8, 55, 22, 1, 3, 22, 4, 5};``    ``int` `n = ``sizeof``(arr)/``sizeof``(arr);``    ``cout << countChanges(arr, n);``    ``return` `0;``}`

## Java

 `// Count minimum changes to``// make array from 1 to n``import` `java.util.Set;``import` `java.util.HashSet;` `class` `GfG``{``    ` `    ``static` `int` `countChanges(``int` `arr[], ``int` `n)``    ``{``        ``// It will contain all initial elements``        ``// of array for log(n) complexity searching``        ``Set s = ``new` `HashSet<>();``    ` `        ``// Inserting all elements in a hash table``        ``for` `(``int` `i = ``0``; i < n; i++)``            ``s.add(arr[i]);``        ` `        ``// Finding elements to be changed``        ``int` `count = ``0``;``        ``for` `(``int` `i = ``1``; i <= n; i++)``            ``if` `(!s.contains(i))``                ``count++;``    ` `        ``return` `count;``    ``}` `    ``// Driver code``    ``public` `static` `void` `main(String []args)``    ``{``        ` `        ``int` `arr[] = {``8``, ``55``, ``22``, ``1``, ``3``, ``22``, ``4``, ``5``};``        ``int` `n = arr.length;` `        ``System.out.println(countChanges(arr, n));``    ``}``}` `// This code is contributed by Rituraj Jain`

## Python 3

 `# Count minimum changes to``# make array from 1 to n` `def` `countChanges(arr, n):` `    ``# it will contain all initial``    ``# elements of array for log(n)``    ``# complexity searching``    ``s ``=` `[]` `    ``# Inserting all elements in a list``    ``for` `i ``in` `range``(n):``        ``s.append(arr[i])``    ` `    ``# Finding elements to be changed``    ``count ``=` `0``    ``for` `i ``in` `range``(``1``, n ``+` `1``) :``        ``if` `i ``not` `in` `s:``            ``count ``+``=` `1` `    ``return` `count` `# Driver Code``if` `__name__ ``=``=` `"__main__"``:``    ``arr ``=` `[``8``, ``55``, ``22``, ``1``, ``3``, ``22``, ``4``, ``5``]``    ``n ``=` `len``(arr)``    ``print``(countChanges(arr, n))` `# This code is contributed``# by ChitraNayal`

## C#

 `// C# program to Count minimum changes to``// make array from 1 to n``using` `System;``using` `System.Collections.Generic;` `class` `GfG``{``    ` `    ``static` `int` `countChanges(``int` `[]arr, ``int` `n)``    ``{``        ``// It will contain all initial elements``        ``// of array for log(n) complexity searching``        ``HashSet<``int``> s = ``new` `HashSet<``int``>();``    ` `        ``// Inserting all elements in a hash table``        ``for` `(``int` `i = 0; i < n; i++)``            ``s.Add(arr[i]);``        ` `        ``// Finding elements to be changed``        ``int` `count = 0;``        ``for` `(``int` `i = 1; i <= n; i++)``            ``if` `(!s.Contains(i))``                ``count++;``    ` `        ``return` `count;``    ``}` `    ``// Driver code``    ``public` `static` `void` `Main(String []args)``    ``{``        ``int` `[]arr = {8, 55, 22, 1, 3, 22, 4, 5};``        ``int` `n = arr.Length;``        ``Console.WriteLine(countChanges(arr, n));``    ``}``}` `// This code is contributed by 29AjayKumar`

## PHP

 ``

## Javascript

 ``
Output:
`3`

Time Complexity: O(n)
Auxiliary Space: O(n)

Attention reader! Don’t stop learning now. Get hold of all the important DSA concepts with the DSA Self Paced Course at a student-friendly price and become industry ready.  To complete your preparation from learning a language to DS Algo and many more,  please refer Complete Interview Preparation Course.

In case you wish to attend live classes with industry experts, please refer Geeks Classes Live

My Personal Notes arrow_drop_up