#101 Page: 1 Name: CS32 Midterm Exam. E01, W15, Phill Conrad, UC Santa Barbara

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1 1 # Page: 1 Name: CS32 Midterm E01, W15, Phill Conrad, UC Santa Barbara Wednesday, 04/30/2015, 9:30am 10:45am Name: Umail umail.ucsb.edu Please write your name above AND AT THE TOP OF EVERY PAGE Be sure you turn in every page of this exam. Each exam is numbered (e.g. #137). Each pages is numbered (e.g. Page 1, Page 2, etc.) The last page clearly says "End of ". This exam is closed book, closed notes, closed mouth, cell phone off You are permitted one sheet of paper (max size 8.5x11") on which to write notes These sheets will be collected with the exam, and might not be returned Please write your name on your notes sheet

2 2 # Page: 2 Name: 1. For these questions, assume 8-bit two's complement representation of negative integers. The left-most bit is the sign bit, with 1 representing negative numbers, and 0 representing positive numbers. a. (2 pts) Given the decimal number -93, what is this number's binary representation in 8-bit two's complement? b. (2 pts) Given the decimal number -1, what is this number's binary representation in 8-bit two's complement? c. (2 pts) Given the decimal number -47, what is this number's binary representation in 8-bit two's complement? d. (2 pts) Given that 11 is the 8-bit two's complement representation of a number, what is that number in base ten? -67 e. (2 pts) Given that is the 8-bit two's complement representation of a number, what is that number in base ten? -31 f. (2 pts) Given that is the 8-bit two's complement representation of a number, what is that number in base ten? -97

3 3 # Page: 3 Name: 2. Suppose you have an array called a full of n integer values, indexed 0 through n-1. For simplicity, suppose there are no duplicates. You need to implement a function to return the index of a certain key value k if it occurs in the array, or -1 if it does not. As we've discussed, two possible techniques are linear search (which our textbook calls serial search, and binary search. a. (6 pts) Binary search places one additional requirement on the elements of the array. What is this additional requirement? It can be stated in a single sentence. b. (6 pts) Assuming that the array a meets this additional requirement, describe how to apply the binary search algorithm to this problem. Be clear, precise, and concise. DO NOT WRITE CODE OR PSEUDOCODE. Instead, describe the main idea of the algorithm in plain english. Though it is not required, if you wish, you may make reference to a, n and k in your description. c. (6 pts) Linear search has the advantage of not having this extra requirement, and is much easier to code and implement correctly, but has a serious drawback as compared to binary search. Explain what that is. Again, it can be stated in a single sentence but for full credit, you must be as precise as possible in your answer. d. (6 pts) Assuming that the array a does not meet the requirements for binary search, describe how to apply the linear search algorithm to this problem. Be clear, precise, and concise. DO NOT WRITE CODE OR PSEUDOCODE. Instead, describe the main idea of the algorithm in plain english. Though it is not required, if you wish, you may make reference to a, n and k in your description.

4 4 # Page: 4 Name: 3. So far, our discussion of sorting has focused on two main sorting methods: insertion sort, and selection sort. Both of these can be implemented as an "in place" sort one where the values are not copied anywhere outside the array, except to a single temporary variable. As we've discussed, both of these sorting techniques can be implemented "in place" as successive passes, where the sorted array is built up at one end of the array or the other, in a series of n-1 steps. Our practice examples have focussed on doing insertion sort where the sorted array is built left to right, and on selection sort, where the sorted array is built right to left but this is not the only possible implementation. For each of the tables below, fill in the successive steps of the algorithm shown. The first two match what we've done before. The second two check whether you can adapt your understanding of how selection sort and insertion work to a novel situation. Grading for parts (a,b): 1 for each incorrect entry, up to max of 8 Grading for parts (c,d): 1 for each incorrect entry, up to max of 4 a. (8 pts) Sort using insertion sort, building sorted array at start of array (at left, the way we've done it before): [0] [1] [2] [3] [4] b. (8 pts) Sort using selection sort, building sorted array at end of array (at right, the way we've done it before.): [0] [1] [2] [3] [4]

5 5 # Page: 5 Name: c. (4 pts) Sort using insertion sort, building sorted array at END of array (at right, the OPPOSITE of the way we've done it before, but still using the approach used in insertion sort.): [0] [1] [2] [3] [4] d. (4 pts) Sort using selection sort, building sorted array at START of array (at left, the OPPOSITE of the way we've done it before, but still using the approach used in selection sort.): [0] [1] [2] [3] [4]

6 6 # Page: 6 Name: 4. Most of the code we write in this course goes in files that end in.cpp. >But sometimes we worked with each of the following types of files. For each type, explain what its purpose is, and its relationship to.cpp files. DON'T USE TOO MANY WORDS. Write just enough to get the main point across. Excessively verbose answers that stray off point may be penalized. a. (4 pts) Purpose of.h files: b. (4 pts).h files relationship to.cpp files: c. (4 pts) Purpose of.o files: d. (4 pts).o files relationship to.cpp files. e. (4 pts) Purpose of Makefile: f. (4 pts) Relationship of Makefile to.cpp files:

7 7 # Page: 7 Name: 5. At right is a fairly common definition for a C++ struct Nodethat can be used to make a linked list of int values, along with a conventional implementation of a function that prints the value of the linked list, one per line. As a homework assignment, you were asked to rewrite the function as a recursive function, i.e. to do the same thing as this iterative version, but using recursion. BUT THAT'S NOT WHAT I'M ASKING YOU TO DO ON THIS EXAM. So read carefully. struct Node { int data; Node *next; } void printlist(node *head) { for (Node *p=head; p!=null; p=p->next) { cout << p->data << endl; } } a. (10 pts) Write the definition of a C++ function called printlistbackwardsthat also takes a Node *headas its parameter, and prints the list backwards. Given that the struct Nodeonly has nextpointers and no prevpointers, you might think this is impossible, but with recursion is not only possible, it is trivially easy. (Well, if you understand recursion it is.) HINT: If you are stuck, start by writing out the recursive version of printlistwhich prints the list forwards using recursion. Then think about how you could tweak the function to print the list backwards instead. THERE IS ONE MORE PROBLEM ON THE FINAL PAGE!

8 8 # Page: 8 Name: b. (6 pts) Given that there are no prevpointers, there is no straightforward way to print the list backwards without iteration that doesn't involve storing some amount of temporary data that is the same size as the list itself. For example, go might go through the list in the forward direction, and either store the data from the nodes in an array which you then iterate through backwards, or in another linked list that is built in the opposite diretion. So how is it that this is possible with recursion? What is happening "under the hood" that makes this possible? Briefly explain. Hint: "activation record". End of total points=100