instructions.md

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 that 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