List Length with Recursion

Elixir algorithm exercise to practice recursion using tail call optimization

Interesting Resources

• Iteration, Recursion, and Tail-call Optimization in Elixir
• Multi-clause Functions with Pattern Matching and Guards in Elixir
• Elixir Lists

Module Usage

  ListLength.call([]) # Result: 0
  ListLength.call([1, 2, 3]) # Result: 3

Algorithm Explanation

  def call(list), do: get_length(list, 0)

  # Hide the logic with private functions - helps to abstract the logic from the main function
  # Multi-clause functions: overload a function by specifying different clauses to match against - if tail is empty, then return the current accumulator value 
  defp get_length([], acc), do: acc

  # Prepend to a list using the | operator in order to access head and tail - possible due to Elixir nature of having linked lists 
  # Recursively call function and increase accumulator argument until the tail is empty 
  defp get_length([_head | tail], acc), do: get_length(tail, 1 + acc)