93 lines
2.8 KiB
Markdown
93 lines
2.8 KiB
Markdown
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# Bird Count
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Welcome to Bird Count on Exercism's Elixir Track.
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If you need help running the tests or submitting your code, check out `HELP.md`.
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If you get stuck on the exercise, check out `HINTS.md`, but try and solve it without using those first :)
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## Introduction
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## Recursion
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Recursive functions are functions that call themselves.
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A recursive function needs to have at least one _base case_ and at least one _recursive case_.
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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.
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Very often, each case is written in its own function clause.
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```elixir
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# base case
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def count([]), do: 0
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# recursive case
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def count([_head | tail]), do: 1 + count(tail)
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```
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## Instructions
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You're an avid bird watcher that keeps track of how many birds have visited your garden on any given day.
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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.
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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.
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## 1. Check how many birds visited today
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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`.
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```elixir
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BirdCount.today([2, 5, 1])
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# => 2
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```
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## 2. Increment today's count
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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]`.
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```elixir
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BirdCount.increment_day_count([4, 0, 2])
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# => [5, 0, 2]
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```
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## 3. Check if there was a day with no visiting birds
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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.
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```elixir
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BirdCount.has_day_without_birds?([2, 0, 4])
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# => true
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BirdCount.has_day_without_birds?([3, 8, 1, 5])
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# => false
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```
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## 4. Calculate the total number of visiting birds
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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.
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```elixir
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BirdCount.total([4, 0, 9, 0, 5])
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# => 18
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```
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## 5. Calculate the number of busy days
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Some days are busier than others. A busy day is one where five or more birds have visited your garden.
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Implement the `BirdCount.busy_days/1` function. It should take a list of daily bird counts and return the number of busy days.
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```elixir
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BirdCount.busy_days([4, 5, 0, 0, 6])
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# => 2
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```
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## Source
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### Created by
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- @angelikatyborska
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### Contributed to by
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- @neenjaw
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