# JS Algorithm – Fibonacci series

Print out the n-th entry in the fibonacci series. The fibonacci series is an ordering of numbers where each number is the sum of the preceeding two.

For example, the sequence [0, 1, 1, 2, 3, 5, 8, 13, 21, 34] forms the first ten entries of the fibonacci series.

Example:

#### First solution:

fib(4) === 3

``````function fib(n) {
// Initializing result array
let result = [0, 1];

// Go from first position of the array until i < n
for (let i = 0; i < n; i++) {
// Each cycle
// Sum save the sum of current item and last item of the array
let sum = result[i] + result[result.length - 1];

// Adding sum to the array (this will be last position now)
result.push(sum);
}

// Printing fibonacci serie
console.log('fibonacci serie -->', result)

// Returning the result
return result[result.length - 2];
}

fib(4);``````

Result:

#### Second solution:

``````function fib(n) {
// Initializing result array
let result = [0, 1];

for (let i = 2; i <= n; i++) {
// For each cycle

// Getting the last element of the array
const a = result[i - 1];

// getting the penultimate element of the array
const b = result[i - 2];

// Saving the sum of a and b into the array
result.push(a + b);
}

// Returning the result
return result[result.length - 1];
}

fib(4);``````

Result:

#### Third solution:

``````function fib(n) {
// Only when n is 0, 1
if (n < 2) {
return n;
}
// Call the function again with less number
return fib(n - 1) + fib(n - 2);
}

fib(4);
``````

Result:

By Cristina Rojas.