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Alternate Fibonacci Numbers

  • Difficulty Level : Easy
  • Last Updated : 28 Apr, 2021

Give a number N, print alternate fibonacci numbers till n-th Fibonacci.

Examples: 

Input :  N = 7
Output : 0 1 3 8 

Input  : N = 15
Output : 0 1 3 8 21 55 144 377 

Read method 2 in the following article : fibonacci number 

Approach:Using dynamic programming approach. Keep storing the previously calculated fibonacci numbers and using the previous two to store the next fibonacci number. 
 

C++




// Alternate Fibonacci Series using Dynamic Programming
#include <bits/stdc++.h>
using namespace std;
 
void alternateFib(int n)
{
    if (n < 0)
      return;
 
    /* 0th and 1st number of the series are 0 and 1*/
    int f1 = 0;
    int f2 = 1;
 
    cout << f1 << " ";
    for (int i = 2; i <= n; i++) {
         int f3 = f2 + f1;
           
         if (i % 2 == 0)
            cout << f3 << " ";
 
         f1 = f2;
         f2 = f3;
    }
}
 
int main()
{
    int N = 15;
    alternateFib(N);
    return 0;
}

Java




// Alternate Fibonacci Series
// using Dynamic Programming
import java.io.*;
 
class GFG
{
static void alternateFib(int n)
{
    if (n < 0)
    return;
 
    /* 0th and 1st number of the
       series are 0 and 1*/
    int f1 = 0;
    int f2 = 1;
 
    System.out.print(f1 + " ");
    for (int i = 2; i <= n; i++)
    {
        int f3 = f2 + f1;
         
        if (i % 2 == 0)
            System.out.print(f3 + " ");
 
        f1 = f2;
        f2 = f3;
    }
}
 
// Driver Code
public static void main (String[] args)
{
    int N = 15;
    alternateFib(N);
}
}
 
// This code is contributed
// by chandan_jnu.

Python3




# Alternate Fibonacci Series
# using Dynamic Programming
def alternateFib(n):
    if (n < 0):
        return -1;
 
    # 0th and 1st number of
    # the series are 0 and 1
    f1 = 0;
    f2 = 1;
 
    print(f1, end = " ");
    for i in range(2, n + 1):
        f3 = f2 + f1;
         
        if (i % 2 == 0):
            print(f3, end = " ");
 
        f1 = f2;
        f2 = f3;
 
# Driver Code
N = 15;
alternateFib(N);
 
# This code is contributed by mits

C#




// Alternate Fibonacci Series
// using Dynamic Programming
using System;
 
class GFG
{
static void alternateFib(int n)
{
    if (n < 0)
    return;
 
    /* 0th and 1st number of
    the series are 0 and 1*/
    int f1 = 0;
    int f2 = 1;
 
    Console.Write(f1 + " ");
    for (int i = 2; i <= n; i++)
    {
        int f3 = f2 + f1;
         
        if (i % 2 == 0)
            Console.Write(f3 + " ");
 
        f1 = f2;
        f2 = f3;
    }
}
 
// Driver Code
public static void Main ()
{
    int N = 15;
    alternateFib(N);
}
}
 
// This code is contributed
// by chandan_jnu.

PHP




<?php
// Alternate Fibonacci Series
// using Dynamic Programming
function alternateFib($n)
{
    if ($n < 0)
    return;
 
    /* 0th and 1st number of
    the series are 0 and 1*/
    $f1 = 0;
    $f2 = 1;
 
    echo $f1 . " ";
    for ($i = 2; $i <= $n; $i++)
    {
        $f3 = $f2 + $f1;
         
        if ($i % 2 == 0)
            echo $f3 . " ";
 
        $f1 = $f2;
        $f2 = $f3;
    }
}
 
// Driver Code
$N = 15;
alternateFib($N);
 
// This code is contributed by mits
?>

Javascript




<script>
 
// Alternate Fibonacci Series
// using Dynamic Programming
function alternateFib(n)
{
    if (n < 0)
        return;
 
    // 0th and 1st number of the
    // series are 0 and 1
    var f1 = 0;
    var f2 = 1;
 
    document.write(f1 + " ");
    for(i = 2; i <= n; i++)
    {
        var f3 = f2 + f1;
 
        if (i % 2 == 0)
            document.write(f3 + " ");
 
        f1 = f2;
        f2 = f3;
    }
}
 
// Driver Code
var N = 15;
 
alternateFib(N);
 
// This code is contributed by gauravrajput1
 
</script>
Output: 
0 1 3 8 21 55 144 377

 

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


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