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Find the next fibonacci number
  • Difficulty Level : Expert
  • Last Updated : 10 Mar, 2021
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Given a fibonacci number N, the task is to find the next fibonacci number.
Examples: 
 

Input: N = 5 
Output:
8 is the next fibonacci number after 5
Input: N = 3 
Output:
 

 

Approach: The ratio of two adjacent numbers in the Fibonacci series rapidly approaches ((1 + sqrt(5)) / 2). So if N is multiplied by ((1 + sqrt(5)) / 2) and round it, the resultant number will be the next fibonacci number.
Below is the implementation of the above approach: 
 

C++




// C++ implementation of the approach
#include<bits/stdc++.h>
using namespace std;
 
// Function to return the next
// fibonacci number
int nextFibonacci(int n)
{
    double a = n * (1 + sqrt(5)) / 2.0;
    return round(a);
}
 
// Driver code
int main()
{
    int n = 5;
    cout << nextFibonacci(n);
}
 
// This code is contributed by mohit kumar 29

Java




// Java implementation of the approach
class GFG
{
     
    // Function to return the next
    // fibonacci number
    static long nextFibonacci(int n)
    {
        double a = n * (1 + Math.sqrt(5)) / 2.0;
        return Math.round(a);
    }
     
    // Driver code
    public static void main (String[] args)
    {
        int n = 5;
        System.out.println(nextFibonacci(n));
    }
}
 
// This code is contributed by AnkitRai01

Python3




# Python3 implementation of the approach
from math import *
 
# Function to return the next
# fibonacci number
def nextFibonacci(n):
    a = n*(1 + sqrt(5))/2.0
    return round(a)
 
# Driver code
n = 5
print(nextFibonacci(n))

C#




// C# implementation of the approach
using System;
 
class GFG
{
     
    // Function to return the next
    // fibonacci number
    static long nextFibonacci(int n)
    {
        double a = n * (1 + Math.Sqrt(5)) / 2.0;
        return (long)Math.Round(a);
    }
     
    // Driver code
    public static void Main(String[] args)
    {
        int n = 5;
        Console.WriteLine(nextFibonacci(n));
    }
}
 
// This code is contributed by 29AjayKumar

Javascript




<script>
 
// Javascript implementation of the approach
 
// Function to return the next
// fibonacci number
function nextFibonacci(n)
{
    let a = n * (1 + Math.sqrt(5)) / 2.0;
    return Math.round(a);
}
 
// Driver code
  
    let n = 5;
    document.write(nextFibonacci(n));
 
// This code is contributed by Mayank Tyagi
 
</script>
Output: 
8

 

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