Find the next fibonacci number

Last Updated : 10 Mar, 2022

Given a fibonacci number N, the task is to find the next fibonacci number.
Examples:

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

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# 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:

Time Complexity: O(1)

Auxiliary Space: O(1)

Nth Fibonacci Number

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Find the next fibonacci number

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