Stanford CS106A Section Assignment 2 Fibonacci Sequence Solution

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So after solving this and looking at the solution, I definitely made this complicated by trying to incorporate what I learned in Lecture 7. Should have completed this before watching all the stuff about methods! On the up side, I at least go to practice the new stuff. Here is the problem:

Here are the possible solutions:


The solution from the class makes this look pretty simple:

Here is my solution, which incorporates the creation of methods that we learned from Lecture 7. My solution is not as elegant, but it works 🙂 You can also find it on gist.

/* 
 * This is the solution to the Section Handout #2 from the  
 * Stanford CS106A online class
 */

import acm.program.*;

public class FibonacciSequence extends ConsoleProgram {

	private static final int MAX_TERM_VALUE = 10000;

	public void run() {
		println( "This program lists the Fibonacci sequence" );
		int term = 0;
		int i = 0;
		while (term < MAX_TERM_VALUE) {
			term = fib(i);
			if (term < MAX_TERM_VALUE) {
				println(term);
			}
			i++;
		}
	}
	private int fib(int n) {
		//Fib(0) = 0
		//Fib(1) = 1
		//Fib(2) = 1 (0 + 1) = fib(0) + fib(1)
		//Fib(3) = 2 (1 + 1) = fib(1) + fib(2)
		//Fib(4) = 3 (1 + 2) = fib(2) + fib(3) 
		//Fib(5) = 5 (2 + 3) = fib(3) + fib(4)
		if (n==0) {
			return 0;
		}
		if (n==1) {
			return 1;
		}
		if (n>1) {
			return fib(n-1) + fib(n-2);
		}
		return 0; //need to include this in case someone enters in a negative #
	}
}

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  • KarelTheRobot

    Hi Natasha,

    I approached this problem exactly like you that is to create a method…

    However, i dont understand why under the run() method you introduced a new variable ‘term’.

    why didnt you do sth like this :

    public void run() {
    int i = 0;
    while (fibonacci(i)< MAX_TERM_VALUE ) {
    println(fibonacci(i));
    i++;
    }

    }

    as for the private fibonacci method if I don't include the return 0;(for the negaive values) line, the fibonacci method becomes invalid. Any idea why?

    • In your method term = fibonnaci(i). I decided to store it as a variable “term”, but you can also just write “fibonnaci(i)” instead, like you did.

      For the return 0 question, your method has to return something. The computer doesn’t know what to return if there is a negative number if you only cover positive numbers, so that’s why it becomes invalid.

      • Mark C

        Heres what I did (I used different var names):

        
public class fibSequence extends ConsoleProgram {

	private static final int MAX_RESULT_VALUE = 10000;
	private static final int INITIAL_RESULT_VALUE = 0;
	
	public void run() {
		println("The program lists the Fibonacci sequence.");
		int result = 0;
		int prevPrevNum = 0;
		int prevNum = 1;
		println(INITIAL_RESULT_VALUE);
		
		while (true) {
			prevPrevNum = prevNum;
			prevNum = result;
			result = prevPrevNum + prevNum;
			if (result &gt; MAX_RESULT_VALUE) break;
			println(result);
		}
		
	}
}
  • Nathan

    That class example does look simple, I ended up going against a brick wall to get mine, but it looks nifty.

    import acm.program.*;
    import java.awt.*;

    public class DefaultConsole extends ConsoleProgram{
    int MAX_TERM=10000; //cutoff
    int n=0;

    public void run() {
    while ( Fib(n) < MAX_TERM){
    println("Round " + n + ": "+Fib(n));
    n++;
    }
    }
    public int Fib(int n)
    {
    if(n<2)
    return n;
    else
    return (Fib(n-1)+Fib(n-2));

    }
    }

  • Am I only one to see fault with the official solution as given? Becuase the condition is set using t1, the program prints a couple of numbers bigger than 10000 before it stops. I solve this by making while (true) and putting a break; under the t3 declaration.

    • My solutions are by no means the “official” ones. I did these when I first started programming, and I would probably have completely different solutions if I went back and solved these today. So yes, there are definitely flaws there, so great job for noticing 🙂