Leaping Lemur

Whiteboard: Medium
Challenge: Easier
Concepts: Loops, Lists
Download: leaping-lemur.zip
Solution: Leaping Lemur: Solution

A lemur wants to jump across a span in the forest on branches. She can jump 1 or 2 branches at a time. Unfortunately, some of the branches are on dead trees, and she can’t use those branches to jump.

For example:

The black circles are dead branches. In this example, the lemur starts on the first branch, and jumps 1 to branch #2 (she can’t jump 2 to branch #3, as it’s dead). She then jumps from 2 to 4 and from 4 to 6. As she ends up on the last branch, she’s finished.

The first and last branch will always be alive, and there will never be two dead branches in a row (that is, it will always be possible for her to make this trip).

Your challenge is to calculate how many jumps she needs to make.

Code

You’ll be given a list of the branches, like:

[0, 0, 1, 0, 1, 0]

0 represents alive branches and 1 represents dead branches. The lemur starts on the first branch in the list (index 0) and is finished when she reaches the last branch in the list.

Write a function that returns the number of jumps needed:

>>> lemur([0])
0

>>> lemur([0, 0])
1

>>> lemur([0, 0, 0])
1

>>> lemur([0, 1, 0])
1

>>> lemur([0, 0, 1, 0])
2

>>> lemur([0, 0, 0, 0, 1, 0, 0, 1, 0])
5

We’ve written a stub function for you. Implement it:

lemur.py

def  lemur(branches):
    """Return number of jumps needed."""

    assert branches[0] == 0, "First branch must be alive"
    assert branches[-1] == 0, "Last branch must be alive"