Large Fibonacci Numbers in Java

1.2

Given a number n, find n-th Fibonacci Number. Note that n may be large.

Examples:

Input : 100
Output : 218922995834555169026

Input : 500
Output : 8616829160023845073278831216566478809594
         1068326060883324529903470149056115823592
         713458328176574447204501

Prerequisite : BigInteger Class in Java, Fibonacci numbers

Fibonacci of large number may contain more than 100 digits, it can be easily handled by BigInteger in Java. BigInteger class is used for mathematical operation which involves very big integer calculations that are outside the limit of all available primitive data types.

// Java program to compute n-th Fibonacci
// number where n may be large.
import java.io.*;
import java.util.*;
import java.math.*;

public class Fibonacci
{
    // Returns n-th Fibonacci number
    static BigInteger fib(int n)
    {
        BigInteger a = BigInteger.valueOf(0);
        BigInteger b = BigInteger.valueOf(1);
        BigInteger c = BigInteger.valueOf(1);
        for (int j=2 ; j<=n ; j++)
        {
            c =  a.add(b);
            a = b;
            b = c;
        }

        return (a);
    }

    public static void main(String[] args)
    {
        int n = 1000;
        System.out.println("Fibonacci of " + n +
            "th term" + " " +"is" +" " + fib(n));
    }
}

Output:

268638100244853593861467272021429239676
166093189869523401231759976179817002478
816893383696544833565641918278561614433
563129766736422103503246348504103776803
673341511728991697231970827639856157644
50078474174626

Note that the above solution takes O(n) time, we can find n-th Fibonacci number in O(Log n) time. As an exercise, find n-th Fibonacci number for large n in O(Log n) time.

This article is contributed by Pramod Kumar. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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