---
title: Eboard 39  Merge Sort
number: 39
section: eboards
held: 2017-12-01
---
CSC 151.01, Class 39:  Merge Sort
=================================

_Overview_

* Preliminaries
    * Notes and news
    * Upcoming work
    * Extra credit
    * Notes on exam 4
    * Questions
* Lab
* Debrief

### News / Etc.

* I hope to have tentative project grades to you by Monday (ignoring the
  presentation component).
* We will discuss the form of the final Monday.
* I will have all your grades to you Monday of finals week.

### Upcoming work

* [Writeup for class 38](../writeups/writeup38) due TONIGHT at 10:30 p.m.
    * Exercise 5.
    * To: <csc151-01-grader@grinnell.edu>
    * Subject: CSC 151.01 Writeup 38 (YOUR NAMES)
* [Writeup for class 39](../writeups/writeup39) due Monday at 10:30 p.m.
    * Exercises 4f, 4g, and 4h
    * To: <csc151-01-grader@grinnell.edu>
    * Subject: CSC 151.01 Writeup 39 (YOUR NAMES)
* [Exam 4](../exams/exam04) 
    * Prologue due TONIGHT
    * Exam due Tuesday
    * Cover sheets due Wednesday
    * Epilogues due Wednesday.
* No more readings.
* No more quizzes (after today).

### Extra credit (Academic/Artistic)

* CS Extras Thursday: Summer opportunities in CS.

### Extra credit (Peer)

* Jazz Ensemble Concert TONIGHT at 7:30 p.m.
* Chamber Ensembles Saturday at 4:00 p.m.

### Extra credit (Misc)

* Mental Health Campus Resource Fair.  Friday at 4pm in JRC 209.
* Newtown movie Tuesday night.
    * Whoops!  If you see the movie, you can have an extra day on Exam 4.

### Other good things

* Swim meet this weekend.  (Friday at ???.  Saturday at ???.)
* One acts this weekend.
* YGB concert Saturday at 2p.m.
* Collegium Concert Sunday at 2:00 p.m.
* Festival of trees Friday at Drake.

### Notes on exam 4

I have responded to most of the prologues that I have received.  Here
are some common notes.

Problem 1 

* You can't just add counters or use the debugger, since many of the "expensive" procedures are built in.  
* Hence, you'll need to think about which procedures are "slow" (in that they look at the whole list).  
* You may want to make a list of the procedures each calls and think about whether each is "fast" or "slow".

Problem 2 

* I'd recommend direct recursion without an accompanying "tally".  
* I'd recommend that you use `pair?` rather than `list?` to check 
  whether something is a sublist.  (We did say that the input was
  well formed.)

Problem 3 

* No changing the vector.
* No using vector append.  
* No using lists.

Problem 4 

* Remember that you need to use binary search.  
* "use binary search" means "use the approach" not "call the procedure"
* Do not change the vector.

Problem 5

* The hard part of the problem is part e.
* You need to write about this problem even if you decide not to do it.

Other

* The most common answer to Q3: "I'm going to do problem 6 because I enjoy whatzitdos and dislike trees."
* The second most common answer: "I don't really like whatzitdos, but I like trees even less."

### Questions

Quiz
----

Lab
---

Please refresh when you do problem 4.

Sorry about the typos.  I keep forgetting that I renamed procedures this
semester.

Writeup: 4fgh  RELOAD BEFORE YOU DO THESE PROBLEMS!

Debrief
-------

How many times is `merge` called in `(merge '(1 2 3 4) '(5 6 7 8) <=)`?

How many times is `merge` called in `(merge '(1 3 5 7) '(2 4 6 8) <=)`?

Why aren't the numbers the same?