This document discusses data structures in Elixir, focusing on queues as an example. It defines a queue as a FIFO data structure and shows how to implement one using two lists to represent the front and back of the queue. Pushing and popping from the queue have O(1) time complexity when using this two-list approach. It also notes that Erlang's built-in :queue function employs this two-list technique and recommends using it for queues in Elixir. The document concludes by mentioning other data structures like red-black trees available in Elixir and tips for measuring performance and avoiding unnecessary list usage.

1. DATA STRUCTURE IN ELIXIR
PRESENTED BY MASATAM

2. ABOUT ME
▶ Name: MasaTam
▶ twitter: @masatam81
▶ Company: Retrieva, Inc.
▶ Academic: M.Eng in CS
at Oregon State Univ.
▶ Area(now): Speech Recognition, NLP
▶ Area(past): System dev, Game dev

3. DATA STRUCTURE
▶ Algorithm + Data Structure = programs
(Niklaus Wirth, 1976)
▶ “Purely Functional Data Structures” by Chris Okasaki

4. QUEUE
•FIFO data structure

5. QUEUE
•FIFO data structure
• push

6. QUEUE
•FIFO data structure
• push
1

7. QUEUE
•FIFO data structure
• push
1

8. QUEUE
•FIFO data structure
• push
1
2

9. QUEUE
•FIFO data structure
• push
1 2
3

10. QUEUE
•FIFO data structure
• push
1 2 3

11. QUEUE
•FIFO data structure
• pop
1 2 3

12. QUEUE
•FIFO data structure
• pop
2 3
1

13. QUEUE
•Adding a new item into the back of list

14. QUEUE
•Adding a new item into the back of list

17. QUEUE
•Adding a new item into the back of list
•Reverse the list?

18. QUEUE
•Adding a new item into the back of list
•Reverse the list?
• Not too bad if poped only after pushing all
items

19. QUEUE
•Solution: use two lists
OUT
IN

20. QUEUE
•Solution: use two lists
• push
OUT
IN

21. QUEUE
•Solution: use two lists
• push
OUT
IN
1

22. QUEUE
•Solution: use two lists
• push
OUT
IN
12

23. QUEUE
•Solution: use two lists
• push
OUT
IN
2 1

24. QUEUE
•Solution: use two lists
• pop
OUT
IN
2 1

25. QUEUE
•Solution: use two lists
• pop
OUT
IN
1 2
reverse

26. QUEUE
•Solution: use two lists
• pop
OUT
IN
21

27. QUEUE
•Solution: use two lists
• push
OUT
IN
2
3

28. QUEUE
•Solution: use two lists
• pop
OUT
IN
3
2

29. QUEUE
•Performance

30. QUEUE
•Performance
• Big-O
Push Pop
List
Queue

31. QUEUE
•Performance
• Big-O
Push Pop
List O(n)
Queue O(1)

32. QUEUE
•Performance
• Big-O
Push Pop
List O(n) O(1)
Queue O(1) O(1)*
* amortized

33. QUEUE
•Performance
• Execution time
Push Pop
List
Queue

34. QUEUE
•Performance
• Execution time
Push Pop
List 18.753sec
(100_000)
0.25sec
(10_000_000)
Queue 1.011sec
(10_000_000)
1.198sec
(10_000_000)

35. QUEUE
•Actually, Erlang employs this way!

36. So, using :queue is the easiest way

37. ERLANG QUEUE
otp/lib/stdlib/src/queue.erl
:queue

38. ERLANG QUEUE
otp/lib/stdlib/src/queue.erl
:queue

39. ERLANG QUEUE REVERSE

40. OTHER DATA STRUCTURE PREPARED
• Red-Black tree
• SplayHeap

41. TIPS
• BenchFella
• to mesure the performance,
especially executuin times.

42. TIPS
• Avoid to use structure if possible

43. TIPS
• Tail call

44. TIPS
•How to add comparator

45. CONCLUSION
• Lists are not always the best choice.
• Use appropriate one deppending on your needs.
• check otp/stdlib/src to find the best data structure.
• Source code
https://github.com/muramasa8191/dataStructureEx