Goals

Overview

This homework is about sorting. You will implement the tree sort algorithm to help you learn about binary search trees (BSTs) and sorting algorithms.

There are no starter files.

Outline of a solution

👌 Okay to copy/adapt anything you see in these two screenshot images. (You may not copy code from lecture or anywhere else.)

Demonstration

#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <assert.h>
#include "sorts.h"

void _print_array(int* array, size_t size, const char* title) {
    printf("%s\n", title);
    for(int i = 0; i < size; i++) {
        printf("%d ", array[i]);
    }
    printf("\n\n");
}

int main(int argc, char* argv[]) {

    // Demonstrate create_bst(…)
    BST bst = create_bst((int[7]) { 4, 2, 6, 1, 3, 5, 7 }, 7);
    assert(bst.root        != NULL && bst.root->value        == 4);
    assert(bst.root->left  != NULL && bst.root->left->value  == 2);
    assert(bst.root->right != NULL && bst.root->right->value == 6);
    empty_bst(&bst);

    // Demonstrate tree_sort_array(…)
    int array1[] = { 5, 4, 2, 1, 7, 6, 3 };
    size_t size1 = sizeof(array1) / sizeof(*array1);  // # of elements
    _print_array(array1, size1, "Before tree_sort_array(array1)");
    tree_sort_array(array1, size1);
    _print_array(array1, size1, "After  tree_sort_array(array1)");

    return EXIT_SUCCESS;
}
/* vim: set tabstop=4 shiftwidth=4 fileencoding=utf-8 noexpandtab: */

Output

Before tree_sort_array(array1)
5 4 2 1 7 6 3

After  tree_sort_array(array1)
1 2 3 4 5 6 7

Requirements

Submit

To submit HW15 from within your hw15 directory, type 264submit HW15 sorts.h sorts.c test_sorts.c miniunit.h log_macros.h Makefile

Q&A

1. Where's the starter code? How am I supposed to start?
   Learning to program in C entails learning to set up your files and code your project to meet a specification—without being given step-by-step instructions. That said, here is a general process you can use for doing that.
   How to do any coding homework in ECE 264
   1. First, identify the files you are responsible for producing. In this case, there are four files: sorts.c, sorts.h, test_sorts.c, and expected.txt. Create an (almost) empty file for each.
   2. In the .c and .h files, add a Vim modeline. (Tip: In Vim on ecegrid, type newc and press Tab to get a skeleton file, including the modeline. Remove any #include statements or anything else that isn't needed or allowed.)
   3. In the .h file (sorts.h), add an include guard.
   4. Create your makefile. This is optional, but recommended. You do not need to use miniunit.h or log_macros.h in order to use make (but you may if you wish).
   5. Submit. Your code is nearly empty, but this gives you a backup.
      make submit (or 264submit sorts.h sorts.c test_sorts.c miniunit.h log_macros.h Makefile for Luddites).
   6. Decide on a general order in which to implement the various parts of the assignment. For HW15, you could do the three parts in any order. If you have no opinion, we lightly suggest doing in this order: ①tree_sort_array(…), ②quick_sort_array(…). But again, it's up to you.
   7. In your test code file (test_sorts.c), create your first test.
   8. Write one very simple test (e.g., sort empty array). At this point, your sorts.c should have no useful code in it.
   9. Write just enough code in sorts.c to pass your easy test.
   10. Run your test (e.g., make test (or ./test_sorts for Luddites). Hopefully, your simple test passes. This step is to test the mechanics of your testing, and verify that you have the correct function signatures and such.
   11. Add a slightly harder test (e.g., sort array of size one).
   12. Add code to your sorts.c so that both of your tests should pass.
   13. Run your tests. Make any fixes so that both of your tests do pass.
   14. Gradually add tests, extend implementation, run tests, and fix, until one section of your project is complete (e.g., until create_bst(…) is working).
   15. Follow the above steps to complete the rest of HW15.
   16. Re-read the specification—especially the Requirements table—and make sure you have done everything, and your types/fields/functions all match the specification.
   17. Check for gaps in your tests. Make sure you get 100% line coverage from make coverage. This is no guarantee of perfection, but if you don't have 100% coverage, you need to fix that. Make sure your tests cause every part of your implementation code to be executed.
   18. Think through your tests carefully. Make sure you have covered all:
       • “edge cases” – extreme values
       • “corner cases” – values that cause your code to behave differently
       • “special cases” – exceptions to normal functionality described in the specification
       • "easy cases" – easy for you to understand
       (Note: These are not standard terms.)
2. Can I add helper functions to sorts.c?
   Yes. Make sure the names begin with "_".
3. Is there a warm-up?
   No.
4. Should I use recursion for the BST operations (create_bst(…), tree_sort_array(…), and empty_bst(…))?
   
   Short answer: Yes.
   Long answer: All of these things can be accomplished without recursion, using only while loops. However, those methods are messier.
   The methods demonstrated in class (see snippets) use recursion, and that is what we recommend.
5. How do I create a BST? … delete a BST?
   
   To create a BST, start with an empty BST (root = NULL) and then insert each element you wish to add.
   To delete a BST, delete the left and right subtree (recursively). Then, free the root.
6. What is “in-order traversal”?
   
   With in-order traversal means you “visit” (i.e., do something with) the left subtree, then the root, and finally the right subtree. In that example, “visit” meant printing the value of a node. For a BST, this results in printing the values in order.
   You will learn a bit more about tree traversals later, but for HW15, this is all you need to know.
   Example:
   In the print_bst(Node* root) function in the snippet:

   1. Print the left subtree by calling print_bst(root -> left)recursively.
   2. Print the root by calling printf("%d\n", root -> value).
   3. Print the right subtree by calling print_bst(root -> right)recursively.
   If the tree has zero nodes (i.e., empty), we do nothing.
   

   If the tree has one node (i.e., root has no children):

   1. print_bst(root -> left) has no effect.
   2. printf("%d ", root -> value) prints 4 .
   3. print_bst(root -> right) has no effect.
   

   If the tree has three nodes (i.e., root has children but no grandchildren):

   1. print_bst(root -> left) prints 2 .
   2. printf("%d ", root -> value) prints 4 .
   3. print_bst(root -> right) prints 6 .

   Altogether, it prints 2 4 6 .
   

   If the tree has seven nodes (i.e., root has children AND grandchildren):

   1. print_bst(root -> left) prints 1 2 3 .
   2. printf("%d ", root -> value) prints 4 .
   3. print_bst(root -> right) prints 5 6 7 .

   Altogether, it prints 1 2 3 4 5 6 7 .
   For tree_sort_array(…), you are following the same process, except instead of printing a value with printf(…), you store it in the array.

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