Algorithm 101: 3 Ways to Get the Fibonacci Sequence

#algorithms #javascript #beginners #fibonacci

In mathematics, the Fibonacci numbers, commonly denoted Fn, form a sequence, called the Fibonacci sequence, such that each number is the sum of the two preceding ones, starting from 0 and 1. - Wikipedia

In this article, we don't want to just return the nth term of a sequence, but we want to return the whole sequence as an array depending on the starting points given. Our counting follows the image below:


fibonacci(8); // 21

We are already used to the function call above usually achieved by the code below:


      function fibonacci(n) {
        let firstNum = 0;
        let secondNum = 1;
        let sum = 0;

        for (let i = 0; i <= n - 2; i++) {
          sum = firstNum + secondNum;
          firstNum = secondNum;
          secondNum = sum;
        }

        return sum;
      }

Now, we want to move a little further to returning the whole sequence depending on the starting points (array of 2 numbers) and the limit (nth term) given.


fibonacciSequence([0, 1], 9); //[ 0, 1, 1, 2, 3, 5, 8, 13, 21, 34 ]

fibonacciSequence([10, 20], 9); //[ 10, 20, 30, 50, 80, 130, 210, 340, 550, 890 ]

Prerequisite

To benefit from this article, you need to possess basic understanding of javascript's arithmetic and array methods.

Let's do this!

for...loop

      function fibonacciSequence(array, limit) {
        let finalArray = [...array];

        for (let i = 0; i < limit - 1; i++) {
          let sum = array[0] + array[1];
          finalArray.push(sum);
          array = [array[1], sum];
        }

        return finalArray;
      }

while...loop

      function fibonacciSequence(array, limit) {
        let finalArray = [...array];
        let counter = 0;

        while (counter < limit - 1) {
          let sum = array[0] + array[1];
          finalArray.push(sum);
          array = [array[1], sum];
          counter++;
        }

        return finalArray;
      }

do...while...loop

      function fibonacciSequence(array, limit) {
        let finalArray = [...array];
        let counter = 0;

        do {
          let sum = array[0] + array[1];
          finalArray.push(sum);
          array = [array[1], sum];
          counter++;
        } while (counter < limit - 1);

        return finalArray;
      }