CS32 Final Exam. E03, F15, Phill Conrad, UC Santa Barbara

Transcription

1 1 #1 Page: 1 Name: CS32 Final E03, F15, Phill Conrad, UC Santa Barbara Thursday, 12/10/2015, noon 3pm 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. 37). 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 1. 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. (2 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. (2 pts) What is the big-o notation for the worse case running time of binary search on an n element array? c. (2 pts) What is the big-o notation for the worse case running time of linear search on an n element array?

2 2 #1 Page: 2 Name: 2. 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 -13, what is this number's binary representation in 8-bit two's complement? b. (2 pts) Given the decimal number -53, what is this number's binary representation in 8-bit two's complement? c. (2 pts) Given that is the 8-bit two's complement representation of a number, what is that number in base ten? -27 d. (2 pts) Given that is the 8-bit two's complement representation of a number, what is that number in base ten? -5 e. (2 pts) Given that is the 8-bit two's complement representation of a number, what is that number in base ten? -43

3 3 #1 Page: 3 Name: 3. (5 pts) 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; 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.

4 4 #1 Page: 4 Name: 4. (5 pts) This question refers back to the question just before this one on the exam the one about writing a recursive function that prints a list in reverse. 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, one 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. 5. (5 pts) At right is some code similar to code that appeared on a homework assignment. My question concerns the * operator on the fifth line of code. Ordinarily a prefix *operator represents a "pointer dereference". Here, however, the variable iteris not a pointer. What feature of C++ is being used here? I'm not looking for a long explanation just for a short phrase 3-6 words or so naming what feature of C++ this is. std::multiset::iterator iter; for (iter = foo.begin(); iter!=foo.end(); iter++) if ( (*iter) < 0 ) {... more code here...

5 5 #1 Page: 5 Name: 6. Some questions about operating systems and tools: a. (3 pts) Briefly: What is the purpose of an operating system? Answer in 8 words or fewer. b. (3 pts) Briefly: In the context of an operating system, what is a process? c. (3 pts) Briefly: In the context of Unix, what is a system call? d. (3 pts) Briefly: What is the circumstance in which a process ends up being a "zombie" process? Be specific. e. (3 pts) Briefly: What is a memory leak? f. (3 pts) Briefly: What tool can help you locate a memory leak? g. (3 pts) Briefly: If you want to use gdb to debug a program, what should you add to CXXFLAGSin your Makefile?

6 6 #1 Page: 6 Name: 7. We now turn our attention to the class LinkedListon the handout that came with your exam. We looked at the QuickSort algorithm that is used to sort an array. A similar algorithm can be used to sort a linked list, with a similar running time. Please first note that the member function addatheadand addattailadd elements to the list. Please fill in the missing lines of code in these functions below as they would appear in the linkedlist.cppfile: a. (3 pts) Fill in exactly ONE missing line of code in addathead: void LinkedList::addAtHead(int data) { Node *n = new Node; n->data = data; this->head = n; if (this->tail==null) this->tail = n; b. (6 pts) Fill in exactly TWO missing lines of code in addattail: void LinkedList::addAtTail(int data) { Node *n = new Node; n->data = data; n->next = NULL; if (this->tail==null) else { this->tail = n;

7 7 #1 Page: 7 Name: 8. (6 pts) The function issorted determines whether or not a linked list is already sorted. Please finish the following function which determines whether a list is already sorted. Be sure that it can run in time O(n), where n is the size of the list. Note that a list of size 0 is already sorted, as is a list of size 1. Be sure you function handles those cases, and does NOT segfault! FOR FULL CREDIT: Confine your answer to filling in only a single line of code in the first blank, and filling in the condition of the for loop. There may be other ways of solving it, but there is a way to solve it in this form, and for full credit, you need to come up with it. bool LinkedList::isSorted() { if (this->head == NULL) for (Node *n=this->head; ; n=n->next) { if (n->next->data < n->data) return false; return true;

8 8 #1 Page: 8 Name: 9. (6 pts) Now, we should be able to use the helper functions already written to put together a quicksort for a linked list. Fill in the missing pieces. void LinkedList::sort() { if (this->issorted()) { return; int pivot = this->head->data; LinkedList left; LinkedList middle; LinkedList right; for (Node *p=this->head; p!=null; p=p->next) { if (p->data < pivot) { left.addattail(p->data); else if (p->data == pivot) { middle.addattail(p->data); else { right.addattail(p->data); left.sort(); right.sort(); // FILL IN THE PARAMETERS this->recycleallmemory(); this->addallattail( ); this->addallattail( ); this->addallattail( );

9 9 #1 Page: 9 Name: 10. (3 pts) In the implementation of LinkedList::sort, we find this line of code: int pivot = this->head->data; Suppose your pair partner were concerned that this->head->datamight produce a segmentation fault due to this->headbeing a null pointer. Write a short, but convincing arrgument (based on the implementation of the functions you have given on this exam) to reassure your pair that this cannot happen. 11. In the member function LinkedList::sort, we see that left,middle,and rightare declared as local variables. a. (3 pts) Will they be stored on the stack or the heap? b. (3 pts) What about the Nodestructs that make up the linked lists that headtail inside each of left,middle,and right: are these on the heap or the stack? 12. For a LinkedListobject representing a list of size n: a. (3 pts) What is the best case running time for the member function sortin terms of big-o notation? NOTE: I said best case, not worst-case. Be careful! b. (3 pts) Explain your answer to the previous question.

10 10 Page: 10 Name: 13. On Page 2 of the handout that came with this exam, you will find correct and complete implementations of the C++ memory-management "big-three" for the LinkedListclass. They are implemented solely in terms of two helper functions, recycleallmemoryand addaddattailas shown here. Your job, after looking over these definitions, will be to fill in missing code in these two helper functions below. a. (6 pts) Fill in the two blanks in addallattail void LinkedList::addAllAtTail(const LinkedList &orig) { for (Node *n= ; n!=null; n=n->next) { b. (6 pts) Fill in the two missing lines in recycleallmemory void LinkedList::recycleAllMemory() { Node *p = while (p!=null) { Node *d = p; p=p->next; this->head = NULL; this->tail = NULL; End of total points=100