# Minimum number of elements to be replaced to make the given array a Fibonacci Sequence

Given an array arr containing N integer elements, the task is to count the minimum number of elements that need to be changed such that all the elements (after proper rearrangement) make first N terms of Fibonacci Series.

Examples:

Input: arr[] = {4, 1, 2, 1, 3, 7}
Output: 2
4 and 7 must be changed to 5 and 8 to make first N(6) terms of Fibonacci series.

Input: arr[] = {5, 3, 1, 1, 2, 8, 11}
Output: 1
11 must be changed to 13.

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

Approach:

• Insert first N elements of Fibonacci series into a multi set.
• Then, traverse the array from left to right and check if the current element is present in multi set.
• If element is present in the multi set then remove it.
• Final answer will be the size of final multi set.

Below is the implementation of the above approach:

## C++

 `// C++ program to find the minimum number ` `// of elements the need to be changed ` `// to get first N numbers of Fibonacci series ` `#include ` `using` `namespace` `std; ` ` `  `// Function that finds minimum changes required ` `int` `fibonacciArray(``int` `arr[], ``int` `n) ` `{ ` `    ``multiset<``int``> s; ` ` `  `    ``// a and b are first two ` `    ``// fibonacci numbers ` `    ``int` `a = 1, b = 1; ` `    ``int` `c; ` ` `  `    ``// insert first n fibonacci elements to set ` `    ``s.insert(a); ` `    ``if` `(n >= 2) ` `        ``s.insert(b); ` ` `  `    ``for` `(``int` `i = 0; i < n - 2; i++) { ` `        ``c = a + b; ` `        ``s.insert(c); ` `        ``a = b; ` `        ``b = c; ` `    ``} ` ` `  `    ``multiset<``int``>::iterator it; ` `    ``for` `(``int` `i = 0; i < n; i++) { ` ` `  `        ``// if fibonacci element is present ` `        ``// in the array then remove it from set ` `        ``it = s.find(arr[i]); ` `        ``if` `(it != s.end()) ` `            ``s.erase(it); ` `    ``} ` ` `  `    ``// return the remaining number of ` `    ``// elements in the set ` `    ``return` `s.size(); ` `} ` ` `  `// Driver code ` `int` `main() ` `{ ` `    ``int` `arr[] = { 3, 1, 21, 4, 2, 1, 8, 9 }; ` `    ``int` `n = ``sizeof``(arr) / ``sizeof``(arr); ` ` `  `    ``cout << fibonacciArray(arr, n); ` ` `  `    ``return` `0; ` `} `

## Java

 `// Java program to find the minimum number  ` `// of elements the need to be changed  ` `// to get first N numbers of Fibonacci series  ` `import` `java.util.*; ` ` `  `class` `geeks ` `{ ` ` `  `    ``// Function that finds minimum changes required ` `    ``public` `static` `int` `fibonacciArray(``int``[] arr, ``int` `n)  ` `    ``{ ` `        ``Set s = ``new` `HashSet(); ` ` `  `        ``// a and b are first two ` `        ``// fibonacci numbers ` `        ``int` `a = ``1``, b = ``1``; ` `        ``int` `c; ` ` `  `        ``// insert first n fibonacci elements to set ` `        ``s.add(a); ` `        ``if` `(n > ``2``) ` `            ``s.add(b); ` ` `  `        ``for` `(``int` `i = ``0``; i < n - ``2``; i++) ` `        ``{ ` `            ``c = a + b; ` `            ``s.add(c); ` `            ``a = b; ` `            ``b = c; ` `        ``} ` ` `  `        ``for` `(``int` `i = ``0``; i < n; i++) ` `        ``{ ` ` `  `            ``// if fibonacci element is present ` `            ``// in the array then remove it from set ` `            ``if` `(s.contains(arr[i])) ` `                ``s.remove(arr[i]); ` `        ``} ` ` `  `        ``// return the remaining number of ` `        ``// elements in the set ` `        ``return` `s.size(); ` `    ``} ` ` `  `    ``// Driver Code ` `    ``public` `static` `void` `main(String[] args)  ` `    ``{ ` `        ``int``[] arr = { ``3``, ``1``, ``21``, ``4``, ``2``, ``1``, ``8``, ``9` `}; ` `        ``int` `n = arr.length; ` ` `  `        ``System.out.print(fibonacciArray(arr, n)); ` `    ``} ` `} ` ` `  `// This code is contributed by ` `// sanjeev2552 `

## Python3

 `# Python3 program to find the minimum number  ` `# of elements the need to be changed  ` `# to get first N numbers of Fibonacci series  ` ` `  `# Function that finds minimum changes required  ` `def` `fibonacciArray(arr, n):  ` ` `  `    ``s ``=` `set``()  ` ` `  `    ``# a and b are first two  ` `    ``# fibonacci numbers  ` `    ``a, b ``=` `1``, ``1` ` `  `    ``# insert first n fibonacci elements to set  ` `    ``s.add(a)  ` `    ``if` `n >``=` `2``:  ` `        ``s.add(b)  ` ` `  `    ``for` `i ``in` `range``(``0``, n ``-` `2``):  ` `        ``c ``=` `a ``+` `b  ` `        ``s.add(c)  ` `        ``a, b ``=` `b, c  ` ` `  `    ``for` `i ``in` `range``(``0``, n):  ` ` `  `        ``# if fibonacci element is present in  ` `        ``# the array then remove it from set  ` `        ``if` `arr[i] ``in` `s:  ` `            ``s.remove(arr[i])  ` ` `  `    ``# return the remaining number  ` `    ``# of elements in the set  ` `    ``return` `len``(s)  ` ` `  `# Driver code  ` `if` `__name__ ``=``=` `"__main__"``:  ` ` `  `    ``arr ``=` `[``3``, ``1``, ``21``, ``4``, ``2``, ``1``, ``8``, ``9``]  ` `    ``n ``=` `len``(arr)  ` ` `  `    ``print``(fibonacciArray(arr, n)) ` ` `  `# This code is contributed by Rituraj Jain `

## C#

 `// C# program to find the minimum number  ` `// of elements the need to be changed  ` `// to get first N numbers of Fibonacci series  ` `using` `System; ` `using` `System.Collections.Generic; ` `     `  `public` `class` `geeks ` `{ ` ` `  `    ``// Function that finds minimum changes required ` `    ``public` `static` `int` `fibonacciArray(``int``[] arr, ``int` `n)  ` `    ``{ ` `        ``HashSet<``int``> s = ``new` `HashSet<``int``>(); ` ` `  `        ``// a and b are first two ` `        ``// fibonacci numbers ` `        ``int` `a = 1, b = 1; ` `        ``int` `c; ` ` `  `        ``// insert first n fibonacci elements to set ` `        ``s.Add(a); ` `        ``if` `(n > 2) ` `            ``s.Add(b); ` ` `  `        ``for` `(``int` `i = 0; i < n - 2; i++) ` `        ``{ ` `            ``c = a + b; ` `            ``s.Add(c); ` `            ``a = b; ` `            ``b = c; ` `        ``} ` ` `  `        ``for` `(``int` `i = 0; i < n; i++) ` `        ``{ ` ` `  `            ``// if fibonacci element is present ` `            ``// in the array then remove it from set ` `            ``if` `(s.Contains(arr[i])) ` `                ``s.Remove(arr[i]); ` `        ``} ` ` `  `        ``// return the remaining number of ` `        ``// elements in the set ` `        ``return` `s.Count; ` `    ``} ` ` `  `    ``// Driver Code ` `    ``public` `static` `void` `Main(String[] args)  ` `    ``{ ` `        ``int``[] arr = { 3, 1, 21, 4, 2, 1, 8, 9 }; ` `        ``int` `n = arr.Length; ` ` `  `        ``Console.WriteLine(fibonacciArray(arr, n)); ` `    ``} ` `} ` ` `  `// This code is contributed by Rajput-Ji `

Output:

```2
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