1. Recursion & Linked Lists

2. Why Recursion & Linked Lists
Important for functional programming

3. Why Recursion & Linked Lists
Important for functional programming
Important for more complex structures
Linked Lists are good practice

4. Why Recursion & Linked Lists
Important for functional programming
Important for more complex structures
Linked Lists are good practice
Can solve some problems better than iteration

5. Challenge
How do we print this in reverse order?

6. Challenge Iterative: for(i = length-1 … 0) cout << retrieveAt(i)
How do we print this in reverse order?
Iterative: for(i = length-1 … 0) cout << retrieveAt(i)
BigO?

7. Challenge
How do we print this in reverse order?
Iterative: for(i = length-1 … 0) //O(n) cout << retrieveAt(i) //O(n)
BigO? O(n2)

8. Challenge Better iterative: Make array of size n
Walk forward, adding items to array
Print array backwards

9. Challenge Better iterative: Make array of size n
Walk forward, adding items to array O(n)
Print array backwards O(n) 6 10 3 15

10. Challenge
Recursive
O(n) time
Only call stack for storage

11. Recursive Setup Bookkeeping needed Pointer for position
Any other parameters
current

12. Recursive Setup Recursive Function Needs Base case : General case :
I know my part of the answer without asking anyone else
General case :
I don’t know the whole answer, but here is one step

13. Print
Print in forward order:
Base case :
If we hit nullptr, stop

14. Print Print in forward order: Base case : General case:
If we hit nullptr, stop
General case:
Print out current->data
Recursively print rest

15. Print
Print in forward order:

16. Print Print in forward order:
Non-member function kicks start recursion

17. getTotal getTotal: Base case : General case:
If at nullptr, answer is 0
General case:
Current value + getTotal from all the rest

18. getTotal
getTotal:

19. retireveAt retrieveAt(index) Base case : General case :
No steps left – return item
General case :
Ask “the next guy” to do one less step, return that

20. Strategy 1 removeLast removeLast Base Case : next to last node
If current->next->next == null Remove next
General Case :
Ask next to removeLast

21. Strategy 1 removeLast removeLast Base Case : next to last node
If current->next->next == null
Remove next
General Case :
Ask next to removeLast
What if only one item???

22. Strategy 2 removeLast removeLast Base Case : on last node
If current->next == null
Delete current
Return null
General Case :
Set current->next to result of removeLast on next
Return current

23. removeLast
Strategy 2
removeLast

24. removeLast
Strategy 2
removeLast

25. removeLast
Strategy 2
removeLast

26. removeLast Print in forward order:
Function always returns current or null
Used to “fix up” node/head that was pointing to current