# Minimum array element changes to make its elements 1 to N

• Difficulty Level : Medium
• Last Updated : 08 Sep, 2022

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 then increment count. The final value of count will be the minimum changes required.

Implementation:

## 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[0]);` `    ``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`

Complexities Analysis:

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

My Personal Notes arrow_drop_up
Related Articles