UNIVERSITY OF MASSACHUSETTS LOWELL Department of Electrical and Computer Engineering EXAM November 2016

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1 UNIVERSITY OF MASSACHUSETTS LOWELL Department of Electrical and Computer Engineering EXAM 2 14 November 2016 Problem Weight Score 1 30 % 2 36 % 3 32 % Bonus 2 % TOTAL 100 % INSTRUCTIONS You may not leave the room until you are finished with the exam. The exam paper must be turned in when you leave. This is a closed book / closed notes exam. Hard-coded constants are allowed on the exam. If your solution is overly complex, you will not receive full credit. All answers must be justified. Clearly show how your answers were obtained. Partial credit will be given only for work that is neat, organized, and easy to follow. Make sure that your cell phone is turned off. Read all questions carefully and completely. If you do not follow instructions, you will lose credit. You may use a calculator, but calculator sharing is not allowed. No scrap paper is allowed. Do all work on the exam paper. USE PENCIL ONLY NO INK! I have read and I understand the instructions given above. NAME

2 Problem 1 Queues EXAM 2 Listed below is the file Queue.h, which defines a queue class that is based on a singly linked list as in Program 6. On the next page, fill in the incomplete definition of the Queue class member function: Enqueue( ). Note that Enqueue() has 2 cases: 1) add the first node to an empty queue, and 2) add a node to a non-empty queue. Be sure use assert( ) to check for memory allocation failures using new. // Q u e u e. h #include "Position.h" typedef Position QueueElem class Queue // Queue class node definition struct Node QueueElem data // The "contents" of the node Node *succ // Link to the successor node Node(): succ(0) Node(const QueueElem &thedata) : data(thedata), succ(0) Queue() : head(0), tail(0) // Default Constructor bool Empty() const return head == 0 // Returns true if empty void Enqueue(const QueueElem &elem) // Add new tail element QueueElem Dequeue() // Remove and return head element QueueElem Head() const // Retrieve but don't remove head element Node *head // Points to head node Node *tail // Points to tail node

3 Problem 1 Queues EXAM 2 void Queue::Enqueue(const QueueElem &elem) // Allocate a new node. Node *newnode = // Validate successful memory allocation. if (head == 0) // Add new node to an empty queue. else head = // Add new node after current tail node. // The new node is the new tail. tail =

4 Problem 2 Find a Path Through a Maze EXAM 2 Fall 2010 Shown below is the pseudo-code for a stack-based algorithm to find a path through a maze. Also shown are the definitions of the Maze and Stack classes from Program 5. On the next page is an incomplete definition of function SolveMaze() that employs this algorithm. Fill in the missing code boxes to complete the SolveMaze() function. 1. Create a position stack 2. Push the start cell position onto the position stack 3. Mark the top of stack position Visited 4. Repeat a. If the top of the stack is the goal position i. return true b. Find an open adjacent cell neighboring the current cell position (one cell to the east, south, west, or north in that order) c. If an open neighbor cell was found i. Push the open neighbor cell s position onto the stack as the new current position ii. Mark the top of stack cell position Visited d. else i. Mark the current cell position Rejected ii. Pop the rejected cell off of the stack iii. if the stack is empty 1. return false Maze Class Definition // Cell States const char Open = ' ' // Open cell const char StartCell = 'S' // Start cell const char GoalCell = 'G' // Goal cell const char Visited = 'V' // Visited cell const char Rejected = R // Rejected Cell class Maze Maze() bool IsOpen(const Position &cellpos) const Position Start() return start Position Goal() return goal void Visit(const Position &p) void Reject(const Position &p) void MarkPathCell(const Position &p) CellState cell[gridsize][gridsize] Position start Position goal other private members not shown Stack Class Definition class Stack struct Node Omitted Members Stack() : tos(0) bool Empty() const return tos == 0 StackElement Top() const void Push(const StackElement &p) StackElement Pop() Node *tos Position Offsets const Position StepEast = Position(0, +1) // One step east const Position StepSouth = Position(+1, 0) // One step south const Position StepWest = Position(0, -1) // One step west const Position StepNorth = Position(-1, 0) // One step north

5 Problem 2 Find a Path Through a Maze EXAM 2 Fall 2010 bool FindOpenNeighbor(Maze &maze, Position curpos, Position &pos) // Find an open neighbor cell of curpos pos = curpos + StepEast if (!maze.isopen(pos)) pos = curpos + StepSouth if (!maze.isopen(pos)) pos = curpos + StepWest if (!maze.isopen(pos)) pos = curpos + StepNorth return maze.isopen(pos) bool SolveMaze(Maze &maze, Stack &posstack) // Move to the start cell. posstack.push(maze.start()) maze.visit(posstack.top()) // Repeatedly find a next move until the goal is reached or no options left for () // If the goal has been reached, return true. if (posstack.top() == maze.goal()) // Not the goal, try to find an open neighbor. Position openneighbor if (FindOpenNeighbor(maze, posstack.top(), openneighbor)) // An open neighbor was found, move there. else // No open neighbor, reject the current position and back up. // If no more places to back up, there is no solution.

6 Problem 3 Singly Linked List EXAM 2 Shown below is the class definition for the linked list class from Program 4. Your job is to fill in the blanks to complete the definition of the member functions Empty( ), Skip( ), and Delete( ). Be sure to use assert( ) to check for invalid list operations, in which case the program should terminate with an error message. typedef Point NodeData Linked List Class Definition //----- C l a s s L i n k e d L i s t class LinkedList // List node class definition class Node NodeData data // The "contents" of the node Node *next // Link to the next node // Node Constructor Functions Node() Node(const NodeData &thedata, Node *const thenext = 0) : data(thedata), next(thenext) // Constructor LinkedList() // True if the list is empty bool Empty() const // True if the current position is beyond the last entry. bool AtEnd() const // Rewind the current entry to the beginning of the list. void Rewind() pred = 0 current = first // Skip to the next entry in the list. void Skip() // Get the contents of the current list entry. NodeData CurrentEntry() const // Insert a new list entry before the current entry. void Insert(const NodeData &d) //Delete the current entry. //The new current entry is the successor of the deleted node. void Delete() Node *first // Points to the first node in the list Node *current // Points to the current node Node *pred // Points to the node preceding the current node.

7 Problem 3 Singly Linked List EXAM 2 NOTE: You may only add where blanks are provided. bool LinkedList::Empty() const return void LinkedList::Skip() pred = current = current->next void LinkedList::Delete() if (pred == 0) // Delete first node delete current else current = // Not first node pred->next = current->next current =