Data Structures, Sample Test 1, with Answers

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1 Data Structures, Sample Test 1, with Answers 1. A doubly linked list is based on the following data: class DoubleList{ // public function declarations here... private: struct DoubleNode{ ListItemType item; // data in the node DoubleNode* next; // points to next node DoubleNode* precede; // points to previous node ; DoubleNode* head; // points to first node ; (a) Write a member function void DoubleList::removeFirstNode() which deletes the first node from a doubly linked list. (b) Assume the DoubleNode* variable curr points to a node in our doubly linked list. Write a few lines of code to remove this node *curr from the list. (Be careful: what should happen if curr is at the beginning or end of the list?) (c) Write a member function DoubleList::DoubleNode* DoubleList::find(int index) which returns a pointer to the node at position index in the doubly linked list. Your function should return NULL if the index is out of range (note our class DoubleList does not have a size data member: how can you determine if index is out of range in this case?)

2 2. What is the output (to the screen) of the following program? Be sure you pay attention to all the cout statements. #include<iostream> int binarysearch(const int anarray[], int first, int last, int value){ cout << "binarysearch: first = " << first << ", last = " << last << ".\n"; if (first>last) return -1; else{ int mid = (first + last)/2; if (value == anarray[mid]) return mid; else if (value < anarray[mid]) return binarysearch(anarray, first, mid-1, value); else return binarysearch(anarray, mid+1, last, value); // end else // end binarysearch int main(){ int a[] = {1,4,5,10,12,18,25,31,107; cout << binarysearch(a,0,8,12) << endl; cout << binarysearch(a,0,8,15) << endl; 3. What is the output of the following program? #include<iostream> #include<exception> int main(){ for (int i=1; i<=3; ++i){ try{ if (i%2 == 0) throw exception(); cout << "i is now " << i << endl; // end try catch (exception e){ cout << "error\n"; // end catch // end for // end main

3 4. Consider the List class with the following private members: class List{ /* public members here... */ private: struct Node{ ListDataType item; // the data of the node Node* next; // points to the next node of the list ; Node* head; // point to first node in the list ; Consider the linked list of ints represented by the following diagram: head NULL (a) Draw a diagram of the above list after the following lines of code have been executed: Node* prev = head->next; Node* nodetoinsert = new Node; nodetoinsert->item = 4; nodetoinsert->next = prev->next; prev->next = nodetoinsert; (b) Assume that the code represented above in part (a) has executed. What is the value of prev->item? (c) In addition to the code above, assume the following code executes. Draw a diagram of the list after this code executes as well. prev = prev->next; prev = prev->next; Node* curr = prev->next; prev->next = curr->next; delete curr; curr = NULL;

4 5. Consider the ADT List operations (a) Create an empty list. (b) Destroy a list. (c) Determine whether a list is empty. (d) Determine the number of items in a list. (e) Insert an item at a given position in the list. (f) Delete the item at a given position in the list. (g) Look at (retrieve) the item at a given position in the list. Using only the ADT List operations (a)-(g) above, describe how to replace an item at a given position on a list with a new item. (So, for example, given the list of integers 0,3,8,9,4,10, if the fourth item is to be replaced with a 7, the new list will be 0,3,8,7,4,10.) You may write your answer in (precise) words, in pseudocode, or in representative C++ code.

5 Answers 1. (a) void DoubleList::removeFirstNode(){ if (head!= NULL){ DoubleNode* temp = head; head = head->next; delete temp; temp = NULL; if (head!= NULL) head->precede = NULL; (b) (c) DoubleNode* prev = curr->precede; DoubleNode* following = curr->next; if (prev!= NULL) prev->next = following; if (following!= NULL) following->precede = prev; delete curr; DoubleList::DoubleNode* DoubleList::find(int index){ if (index<1) return NULL; DoubleNode* curr = head; for (int i=1; i<index; ++i){ if (curr == NULL) return NULL; curr = curr->next; // end for return curr; 2. binarysearch: first = 0, last = 8. 4 binarysearch: first = 0, last = 8. binarysearch: first = 5, last = 8. binarysearch: first = 5, last = 5. binarysearch: first = 5, last = i is now 1 error i is now 3 4. (a) (b) 3 head NULL

6 (c) head NULL 5. Our task is to replace the item at position i in the list with the newitem. First delete the item at position i in the list using ADT operation (f). Then place newitem at position i in the list using ADT operation (e).