Coding Challenge Practice - Question 56

The task is to implement a function that generates a Fibonacci number.

The boilerplate code:

function fib(n){

  if (n === 0) return 0

  if (n === 1) return 1

  return fib(n - 1) + fib(n - 2)

}

The fibonacci sequence starts with ) as the 0th number, and 1 as the 1st number. Every subsequent number is a sum of the previous two.

Start with two variables. One that holds the previous fibonacci number, and one that holds the next fibonacci number.

let prev = 0, curr = 1

Repeatedly update them. The next number is a sum of the previous two.

for(let i = 2, i <= n, i++) {

let next = prev + curr

}

The current becomes the previous, the next becomes the current.

prev = curr

curr = next

This is done till the desired position is reached.

The final code

function fib(n){

  if(n < 0) return undefined;

  if (n === 0) return 0;

  if (n === 1) return 1;



  let prev = 0, curr = 1;



  for(let i = 2; i <= n; i++) {

    let next = prev + curr;

    prev = curr;

    curr = next;

  }

  return curr

}

That's all folks!