- Practice
- Tutorials
- Cracking the Coding Interview
- Recursion: Fibonacci Numbers

# Recursion: Fibonacci Numbers

# Recursion: Fibonacci Numbers

Check out the resources on the page's right side to learn more about recursion. The video tutorial is by Gayle Laakmann McDowell, author of the best-selling interview book Cracking the Coding Interview.

*The Fibonacci Sequence*

The Fibonacci sequence appears in nature all around us, in the arrangement of seeds in a sunflower and the spiral of a nautilus for example.

The Fibonacci sequence begins with and as its first and second terms. After these first two elements, each subsequent element is equal to the sum of the previous two elements.

Programmatically:

Given , return the number in the sequence.

As an example, . The Fibonacci sequence to is . With zero-based indexing, .

**Function Description**

Complete the recursive function in the editor below. It must return the element in the Fibonacci sequence.

fibonacci has the following parameter(s):

*n*: the integer index of the sequence to return

**Input Format**

The input line contains a single integer, .

**Constraints**

**Output Format**

Locked stub code in the editor prints the integer value returned by the function.

**Sample Input**

```
3
```

**Sample Output**

```
2
```

**Explanation**

The Fibonacci sequence begins as follows:

...

We want to know the value of . In the sequence above, evaluates to .