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Given an integer N. The task is to find the Nth odd Fibonacci number.
The odd number fibonacci series is as:
1, 1, 3, 5, 13, 21, 55, 89, 233, 377, 987, 1597………….and so on.
Note: In the above series we have omitted even terms from the general fibonacci sequence.
Examples:
Input: N = 3Output: 3Input: N = 4Output: 5
Approach:
On observing carefully, it can be deduced that every third Fibonacci number is even, so the Nth odd Fibonacci number is the {(3*N+1)/2}th term in the general Fibonacci sequence.
Below is the implementation of the above approach:
C++
// C++ program for Nth odd fibonacci number
#include <bits/stdc++.h>
using namespace std;
// Function to find nth odd fibonacci number
int oddFib(int n)
{
n = (3 * n + 1) / 2;
int a = -1, b = 1, c, i;
for (i = 1; i <= n; i++) {
c = a + b;
a = b;
b = c;
}
return c;
}
// Driver Code
int main()
{
int n = 4;
cout << oddFib(n);
return 0;
}
Java
// Java program for Nth odd fibonacci number
class GFG
{
// Function to find nth odd fibonacci number
static int oddFib(int n)
{
n = (3 * n + 1) / 2;
int a = -1, b = 1, c = 0, i;
for (i = 1; i <= n; i++)
{
c = a + b;
a = b;
b = c;
}
return c;
}
// Driver Code
public static void main (String[] args)
{
int n = 4;
System.out.println(oddFib(n));
}
}
// This code is contributed by AnkitRai01
Python3
# Python3 program for Nth odd fibonacci number
# Function to find nth odd fibonacci number
def oddFib(n):
n = (3 * n + 1) // 2
a = -1
b = 1
c = 0
for i in range(1, n + 1):
c = a + b
a = b
b = c
return c
# Driver Code
n = 4
print(oddFib(n))
# This code is contributed by mohit kumar
C#
// C# program for Nth odd fibonacci number
using System;
class GFG
{
// Function to find nth odd fibonacci number
static int oddFib(int n)
{
n = (3 * n + 1) / 2;
int a = -1, b = 1, c = 0, i;
for (i = 1; i <= n; i++)
{
c = a + b;
a = b;
b = c;
}
return c;
}
// Driver Code
public static void Main (String[] args)
{
int n = 4;
Console.WriteLine(oddFib(n));
}
}
// This code is contributed by 29AjayKumar
Javascript
<script>
// JavaScript program for Nth odd fibonacci number
// Function to find nth odd fibonacci number
function oddFib(n)
{
n = (3 * n + 1) / 2;
var a = -1, b = 1, c, i;
for (i = 1; i <= n; i++) {
c = a + b;
a = b;
b = c;
}
return c;
}
// Driver Code
var n = 4;
document.write(oddFib(n));
</script>
Output:
5
Time Complexity: O(N)
Auxiliary Space: O(1)
Last Updated :13 Mar, 2022
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