Smart Cache

Mix.install([
  {:youtube, github: "brooklinjazz/youtube"},
  {:hidden_cell, github: "brooklinjazz/hidden_cell"},
  {:tested_cell, github: "brooklinjazz/tested_cell"},
  {:utils, path: "#{__DIR__}/../utils"}
])

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Smart Cache

A simple implementation of Fibonacci $fib(n) = fib(n-1) + fib(n - 2)$ is very computationally expensive and creates a lot of duplicated work.

defmodule Fib do
  def of(1), do: 0
  def of(2), do: 1
  def of(n), do: of(n - 1) + of(n - 2)
end

Fib.of(30)

For example, Fib.of(30) calculates Fib.of(29) and Fib.of(28). Which in turn calculates both:

• Fib.of(28) and Fib.of(27).
• Fib.of(27) and Fib.of(26).

Fib.of(30) == Fib.of(29) + Fib.of(28)
Fib.of(29) + Fib.of(28) == Fib.of(28) + Fib.of(27) + Fib.of(27) + Fib.of(26)

You can see that we’re calculating Fib.of(27) twice in only the first step. This issue of duplicating work gets worse and worse the further we get in the execution.

To avoid duplicated work, Use Agent to implement a smart cache for the Fib module above.

Ensure that you smart cache values as they are computed, rather than pre-caching results.

defmodule FibCache do
  def of(n) do
  end
end

Commit Your Progress

Run the following in your command line from the beta_curriculum folder to track and save your progress in a Git commit.

$ git add .
$ git commit -m "finish smart cache exercise"

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