Skip to content
Related Articles

Related Articles

Improve Article

Find the longest Fibonacci-like subarray of the given array

  • Difficulty Level : Easy
  • Last Updated : 13 May, 2021

Given an array of N elements, the task is to find the longest subarray which is Fibonacci-like. 
A Fibonacci-like sub-array is defined as an array in which: 
 

A[i]=A[i-1]+A[i-2] where i>2

and, A[1] and A[2] can be anything.

Examples: 
 

Input : N = 5, arr[] = {2, 4, 6, 10, 2}
Output : 4
The sub-array 2, 4, 6, 10 is Fibonacci like.

Input : N = 3, arr[] = {0, 0, 0}
Output : 3
The entire array is Fibonacci-like.

 

Approach:
The idea is to observe that any array of length of less than or equal to 2 is Fibonacci-like. Now, for arrays of length greater than 2:
 

  1. Maintain a variable len initialized to 2 and a variable mx to store the maximum length so far.
  2. Start traversing the array from 3rd index.
  3. If the fibonacci like array can be extended for this index, i.e. if a[i] = a[i-1] + a[i-2] 
    • Then increment the value of variable len by 1.
    • Otherwise reinitialize the variable len to 2.
    • Store the maximum of mx and len in the variable mx for current iteration.

Below is the implementation of the above approach: 
 



C++




// C++ program to find length of longest
// Fibonacci-like subarray
 
#include <bits/stdc++.h>
using namespace std;
 
// Function to find the length of the
// longest Fibonacci-like subarray
int longestFibonacciSubarray(int n, int a[])
{
    // Any 2 terms are Fibonacci-like
    if (n <= 2)
        return n;
     
    int len = 2;
     
    int mx = INT_MIN;
     
    for (int i = 2; i < n; i++) {
         
        // If previous subarray can be extended
        if (a[i] == a[i - 1] + a[i - 2])
            len++;
             
        // Any 2 terms are Fibonacci-like
        else
            len = 2;
             
        // Find the maximum length
        mx = max(mx, len);
    }
     
    return mx;
}
 
// Driver Code
int main()
{
    int n = 5;
    int a[] = {2, 4, 6, 10, 2};
     
    cout << longestFibonacciSubarray(n, a);
     
    return 0;
}

Java




// Java program to find length of longest
// Fibonacci-like subarray
class GFG
{
     
    // Function to find the length of the
    // longest Fibonacci-like subarray
    static int longestFibonacciSubarray(int n, int a[])
    {
        // Any 2 terms are Fibonacci-like
        if (n <= 2)
            return n;
         
        int len = 2;
         
        int mx = Integer.MIN_VALUE;
         
        for (int i = 2; i < n; i++)
        {
             
            // If previous subarray can be extended
            if (a[i] == a[i - 1] + a[i - 2])
                len++;
                 
            // Any 2 terms are Fibonacci-like
            else
                len = 2;
                 
            // Find the maximum length
            mx = Math.max(mx, len);
        }
        return mx;
    }
     
    // Driver Code
    public static void main (String[] args)
    {
        int n = 5;
        int a[] = {2, 4, 6, 10, 2};
         
        System.out.println(longestFibonacciSubarray(n, a));
    }
}
 
// This code is contributed by Ryuga

Python3




# Python3 program to find Length of
# longest Fibonacci-like subarray
 
# Function to find the Length of the
# longest Fibonacci-like subarray
def longestFibonacciSubarray(n, a):
 
    # Any 2 terms are Fibonacci-like
    if (n <= 2):
        return n
     
    Len = 2
     
    mx = -10**9
     
    for i in range(2, n):
         
        # If previous subarray can be extended
        if (a[i] == a[i - 1] + a[i - 2]):
            Len += 1
             
        # Any 2 terms are Fibonacci-like
        else:
            Len = 2
             
        # Find the maximum Length
        mx = max(mx, Len)
     
    return mx
 
# Driver Code
n = 5
a = [2, 4, 6, 10, 2]
 
print(longestFibonacciSubarray(n, a))
 
# This code is contributed by Mohit Kumar

C#




// C# program to find length of longest
// Fibonacci-like subarray
using System;
 
class GFG
{
     
    // Function to find the length of the
    // longest Fibonacci-like subarray
    static int longestFibonacciSubarray(int n, int[] a)
    {
        // Any 2 terms are Fibonacci-like
        if (n <= 2)
            return n;
         
        int len = 2;
         
        int mx = int.MinValue;
         
        for (int i = 2; i < n; i++)
        {
             
            // If previous subarray can be extended
            if (a[i] == a[i - 1] + a[i - 2])
                len++;
                 
            // Any 2 terms are Fibonacci-like
            else
                len = 2;
                 
            // Find the maximum length
            mx = Math.Max(mx, len);
        }
        return mx;
    }
     
    // Driver Code
    public static void Main ()
    {
        int n = 5;
        int[] a = {2, 4, 6, 10, 2};
         
        Console.WriteLine(longestFibonacciSubarray(n, a));
    }
}
 
// This code is contributed by Code_Mech.

PHP




<?php
// PHP program to find length of longest
// Fibonacci-like subarray
 
// Function to find the length of the
// longest Fibonacci-like subarray
function longestFibonacciSubarray($n, $a)
{
    // Any 2 terms are Fibonacci-like
    if ($n <= 2)
        return $n;
     
    $len = 2;
     
    $mx = PHP_INT_MIN;
     
    for ($i = 2; $i < $n; $i++)
    {
         
        // If previous subarray can be extended
        if ($a[$i] == $a[$i - 1] + $a[$i - 2])
            $len++;
             
        // Any 2 terms are Fibonacci-like
        else
            $len = 2;
             
        // Find the maximum length
        $mx = max($mx, $len);
    }
     
    return $mx;
}
 
// Driver Code
$n = 5;
$a = array(2, 4, 6, 10, 2);
     
echo longestFibonacciSubarray($n, $a);
 
// This code is contributed
// by Akanksha Rai   
?>

Javascript




<script>
 
// javascript program to find length of longest
// Fibonacci-like subarray
 
     
    // Function to find the length of the
    // longest Fibonacci-like subarray
    function longestFibonacciSubarray( n,  a)
    {
        // Any 2 terms are Fibonacci-like
        if (n <= 2)
            return n;
         
        var len = 2;
         
        var mx = Number.MIN_VALUE;
  
         
        for (var i = 2; i < n; i++)
        {
             
            // If previous subarray can be extended
            if (a[i] == a[i - 1] + a[i - 2])
                len++;
                 
            // Any 2 terms are Fibonacci-like
            else
                len = 2;
                 
            // Find the maximum length
            mx = Math.max(mx, len);
        }
        return mx;
    }
     
    // Driver Code
 
        var n = 5;
        var a = [2, 4, 6, 10, 2];
         
        document.write(longestFibonacciSubarray(n, a));
   
  // This code is contributed by bunnyram19.
</script>
Output: 
4

 

Time Complexity: O(N) 
Auxiliary Space: O(1)
 

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 experts, please refer DSA Live Classes for Working Professionals and Competitive Programming Live for Students.




My Personal Notes arrow_drop_up
Recommended Articles
Page :