# Check whether Array represents a Fibonacci Series or not

Given an array arr[] consisting of N integers, the task is to check whether a Fibonacci series can be formed using all the array elements or not. If possible, print “Yes”. Otherwise, print “No”.

Examples:

Input: arr[] = { 8, 3, 5, 13 }
Output: Yes
Explanation:
Rearrange given array as {3, 5, 8, 13} and these numbers form Fibonacci series.

Input: arr[] = { 2, 3, 5, 11 }
Output: No
Explanation:
The given array elements do not form a Fibonacci series.

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

Approach:
In order to solve the problem mentioned above, the main idea is to sort the given array. After sorting, check if every element is equal to the sum of the previous 2 elements. If so, then the array elements form a Fibonacci series.

Below is the implementation of the above approach:

## C++

 `// C++ program to check if the ` `// elements of a given array ` `// can form a Fibonacci Series ` ` `  `#include ` `using` `namespace` `std; ` ` `  `// Returns true if a permutation ` `// of arr[0..n-1] can form a ` `// Fibonacci Series ` `bool` `checkIsFibonacci(``int` `arr[], ``int` `n) ` `{ ` `    ``if` `(n == 1 || n == 2) ` `        ``return` `true``; ` ` `  `    ``// Sort array ` `    ``sort(arr, arr + n); ` ` `  `    ``// After sorting, check if every ` `    ``// element is equal to the ` `    ``// sum of previous 2 elements ` ` `  `    ``for` `(``int` `i = 2; i < n; i++) ` `        ``if` `((arr[i - 1] + arr[i - 2]) ` `            ``!= arr[i]) ` `            ``return` `false``; ` ` `  `    ``return` `true``; ` `} ` ` `  `// Driver Code ` `int` `main() ` `{ ` `    ``int` `arr[] = { 8, 3, 5, 13 }; ` `    ``int` `n = ``sizeof``(arr) / ``sizeof``(arr[0]); ` ` `  `    ``if` `(checkIsFibonacci(arr, n)) ` `        ``cout << ``"Yes"` `<< endl; ` `    ``else` `        ``cout << ``"No"``; ` ` `  `    ``return` `0; ` `} `

## Java

 `// Java program to check if the elements of  ` `// a given array can form a Fibonacci Series  ` `import` `java. util. Arrays; ` ` `  `class` `GFG{ ` `     `  `// Returns true if a permutation  ` `// of arr[0..n-1] can form a  ` `// Fibonacci Series  ` `public` `static` `boolean` `checkIsFibonacci(``int` `arr[],  ` `                                       ``int` `n)  ` `{  ` `    ``if` `(n == ``1` `|| n == ``2``)  ` `        ``return` `true``;  ` `     `  `    ``// Sort array  ` `    ``Arrays.sort(arr); ` `     `  `    ``// After sorting, check if every  ` `    ``// element is equal to the sum  ` `    ``// of previous 2 elements  ` `    ``for``(``int` `i = ``2``; i < n; i++) ` `    ``{ ` `       ``if` `((arr[i - ``1``] + arr[i - ``2``]) != arr[i])  ` `           ``return` `false``;  ` `    ``}  ` `    ``return` `true``;  ` `}  ` `     `  `// Driver code ` `public` `static` `void` `main(String[] args)  ` `{ ` `    ``int` `arr[] = { ``8``, ``3``, ``5``, ``13` `};  ` `    ``int` `n = arr.length;  ` `     `  `    ``if` `(checkIsFibonacci(arr, n))  ` `        ``System.out.println(``"Yes"``); ` `    ``else` `        ``System.out.println(``"No"``);  ` `} ` `} ` ` `  `// This code is contributed by divyeshrabadiya07 `

## Python3

 `# Python3 program to check if the ` `# elements of a given array ` `# can form a Fibonacci Series ` ` `  `# Returns true if a permutation ` `# of arr[0..n-1] can form a ` `# Fibonacci Series ` `def` `checkIsFibonacci(arr, n) : ` ` `  `    ``if` `(n ``=``=` `1` `or` `n ``=``=` `2``) : ` `        ``return` `True``; ` ` `  `    ``# Sort array ` `    ``arr.sort() ` ` `  `    ``# After sorting, check if every ` `    ``# element is equal to the ` `    ``# sum of previous 2 elements ` ` `  `    ``for` `i ``in` `range``(``2``, n) : ` `        ``if` `((arr[i ``-` `1``] ``+`  `             ``arr[i ``-` `2``])!``=` `arr[i]) : ` `            ``return` `False``; ` ` `  `    ``return` `True``; ` ` `  `# Driver Code ` `if` `__name__ ``=``=` `"__main__"` `: ` ` `  `    ``arr ``=` `[ ``8``, ``3``, ``5``, ``13` `]; ` `    ``n ``=` `len``(arr); ` ` `  `    ``if` `(checkIsFibonacci(arr, n)) : ` `        ``print``(``"Yes"``); ` `    ``else` `: ` `        ``print``(``"No"``); ` ` `  `# This code is contributed by AnkitRai01 `

## C#

 `// C# program to check if the elements of  ` `// a given array can form a fibonacci series  ` `using` `System; ` ` `  `class` `GFG{  ` `     `  `// Returns true if a permutation  ` `// of arr[0..n-1] can form a  ` `// fibonacci series  ` `public` `static` `bool` `checkIsFibonacci(``int` `[]arr,  ` `                                    ``int` `n)  ` `{  ` `    ``if` `(n == 1 || n == 2)  ` `        ``return` `true``;  ` `         `  `    ``// Sort array  ` `    ``Array.Sort(arr);  ` `         `  `    ``// After sorting, check if every  ` `    ``// element is equal to the sum  ` `    ``// of previous 2 elements  ` `    ``for``(``int` `i = 2; i < n; i++)  ` `    ``{  ` `       ``if` `((arr[i - 1] + arr[i - 2]) != arr[i])  ` `           ``return` `false``;  ` `    ``}  ` `    ``return` `true``;  ` `}  ` `         `  `// Driver code  ` `public` `static` `void` `Main(``string``[] args)  ` `{  ` `    ``int` `[]arr = { 8, 3, 5, 13 };  ` `    ``int` `n = arr.Length;  ` `         `  `    ``if` `(checkIsFibonacci(arr, n))  ` `        ``Console.WriteLine(``"Yes"``);  ` `    ``else` `        ``Console.WriteLine(``"No"``);  ` `}  ` `}  ` ` `  `// This code is contributed by AnkitRai01 `

Output:

```Yes
```

Time Complexity: O(N Log N)

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