exercism/elixir/bird-count

Bird Count

Welcome to Bird Count on Exercism's Elixir Track. If you need help running the tests or submitting your code, check out HELP.md. If you get stuck on the exercise, check out HINTS.md, but try and solve it without using those first :)

Introduction

Recursion

Recursive functions are functions that call themselves.

A recursive function needs to have at least one base case and at least one recursive case.

A base case returns a value without calling the function again. A recursive case calls the function again, modifying the input so that it will at some point match the base case.

Very often, each case is written in its own function clause.

# base case
def count([]), do: 0

# recursive case
def count([_head | tail]), do: 1 + count(tail)

Instructions

You're an avid bird watcher that keeps track of how many birds have visited your garden on any given day.

You decided to bring your bird watching to a new level and implement a few tools that will help you track and process the data.

You have chosen to store the data as a list of integers. The first number in the list is the number of birds that visited your garden today, the second yesterday, and so on.

1. Check how many birds visited today

Implement the BirdCount.today/1 function. It should take a list of daily bird counts and return today's count. If the list is empty, it should return nil.

BirdCount.today([2, 5, 1])
# => 2

2. Increment today's count

Implement the BirdCount.increment_day_count/1 function. It should take a list of daily bird counts and increment the today's count by 1. If the list is empty, return [1].

BirdCount.increment_day_count([4, 0, 2])
# => [5, 0, 2]

3. Check if there was a day with no visiting birds

Implement the BirdCount.has_day_without_birds?/1 function. It should take a list of daily bird counts. It should return true if there was at least one day when no birds visited the garden, and false otherwise.

BirdCount.has_day_without_birds?([2, 0, 4])
# => true

BirdCount.has_day_without_birds?([3, 8, 1, 5])
# => false

4. Calculate the total number of visiting birds

Implement the BirdCount.total/1 function. It should take a list of daily bird counts and return the total number that visited your garden since you started collecting the data.

BirdCount.total([4, 0, 9, 0, 5])
# => 18

5. Calculate the number of busy days

Some days are busier than others. A busy day is one where five or more birds have visited your garden.

Implement the BirdCount.busy_days/1 function. It should take a list of daily bird counts and return the number of busy days.

BirdCount.busy_days([4, 5, 0, 0, 6])
# => 2

Source

Created by

• @angelikatyborska

Contributed to by

• @neenjaw