add sort to problems

Author: CarterZenke

sort/.cs50.yml

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+lab50:
+  files:
+    - !exclude "*"
+    - !include sort1
+    - !include sort2
+    - !include sort3
+    - !include sorted5000.txt
+    - !include sorted10000.txt
+    - !include sorted50000.txt
+    - !include reversed5000.txt
+    - !include reversed10000.txt
+    - !include reversed50000.txt
+    - !include random5000.txt
+    - !include random10000.txt
+    - !include random50000.txt
+    - !include answers.txt
+
+check50:
+  files: &check50_files
+    - !exclude "*"
+    - !require answers.txt
+
+submit50:
+  files: *check50_files
+  style: false

sort/README.md

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+# Sort
+
+Analyze three sorting programs to determine which algorithms they use.
+
+## Background
+
+Recall from class a few algorithms in which we can sort a list of numbers: selection sort, bubble sort, and merge sort. 
+
+* Selection sort iterates through the unsorted portions of a list, selecting the smallest element each time and moving it to its correct location. 
+* Bubble sort compares two adjacent values at a time and swaps them if they are in the incorrect order. This continues until the list is sorted.
+* Merge sort divides the list into two repeatedly and then combines the smaller lists back into a larger one in the correct order. 
+
+## Instructions
+
+Provided to you are three sorts, `sort1`, `sort2`, and `sort3`. The three sorts implemented are selection sort, bubble sort, and merge sort. Determine the sorting algorithms each sort implements. 
+
+* `sort1`, `sort2`, and `sort3` are binary files and cannot be opened by the user. To assess which sort implements which algorithm, run the sorts on different lists of values. 
+* Multiple `.txt` files are provided to you. These files contain `n` lines of values, either reversed, shuffled, or sorted. 
+  * For example, `reversed10000.txt` contains 10000 lines of numbers that are reversed from `10000`, while `shuffled100000.txt` contains 100000 lines of numbers that are in random order. 
+* To run the sorts on the text files, in the terminal, run `./[sort_file] [text_file.txt]`. 
+  * For example, to sort `reversed10000.txt` with `sort1`, run `./sort1 reversed10000.txt`. 
+* Record your predictions in `answers.txt`. 
+
+### Hints
+
+* You may find it helpful to time your sorts. To do so, run `time ./[sort_file] [text_file.txt]`. 
+* The different types of `.txt` files may help you determine which sort is which. Consider how each algorithm performs with an already sorted list. How about a reversed list? Or shuffled list? It may help to work through a smaller list of each type and walk through each sorting process. 
+
+{% next %}
+
+## How to Submit
+
+TODO

sort/__init__.py

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+import check50
+from re import search
+from re import findall
+
+@check50.check()
+def exists():
+    """answers.txt exists"""
+    check50.exists("answers.txt")
+
+@check50.check(exists)
+def answers():
+    """answers all questions"""
+    content = open("answers.txt", "r").read()
+    if "TODO" in content:
+        raise check50.Failure("Not all questions answered.")
+
+@check50.check(exists)
+def sorts():
+    """correctly identifies each sort"""
+
+    check50.log("checking that sorts are classified correctly...")
+
+    expected = ["sort1 uses:\s*[Bb][Uu][Bb][Bb][Ll][Ee]", "sort2 uses:\s*[Mm][Ee][Rr][Gg][Ee]", "sort3 uses:\s*[Ss][Ee][Ll][Ee][Cc][Tt][Ii][Oo][Nn]"]
+    actual = open("answers.txt", "r").read()
+
+    for e in expected:
+        if not search(e, actual):
+            raise check50.Failure("Incorrect assignment of sorts.")
+

sort/answers.txt

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+sort1 uses: TODO
+
+How do you know?: TODO
+
+sort2 uses: TODO
+
+How do you know?: TODO
+
+sort3 uses: TODO
+
+How do you know?: TODO