Linked List using a Sentinel

Transcription

1 Linked List using a Sentinel Linked List.h / Linked List.h Using a sentinel for search Created by Enoch Hwang on 2/1/10. Copyright 2010 La Sierra University. All rights reserved. / #include <iostream> using namespace std; class LinkedList{ private: struct ListNode { int data; ListNode next; ; ListNode head; ListNode tail; public: LinkedList(); void InsertNode(int d); bool SearchNode(int d); void PrintList(); bool DeleteNode(int d); ;

2 Linked List.cpp #include "Linked List.h" LinkedList::LinkedList(){ head = NULL; tail = NULL; // constructor void LinkedList::InsertNode(int d){ ListNode np = new ListNode; // allocate memory for new node np >data = d; // put data in new node if(head == NULL){ // empty list special case head = np; // set head and tail pointers tail = np; np >next = NULL; else{ // search for correct location to insert node // set up the sentinal first. This part is almost the same as the code in the Search routine ListNode p = head; // pointer for traversing the list ListNode pp = p; // previous pointer that follows p while (p >data < d) { pp = p; // update previous pointer delete sp; // see where to insert the new node if (p == head) { // insert to head of list np >next = head; head = np; else if (p == sp) { // insert to tail of list tail >next = np; np >next = NULL; tail = np; else { // insert to middle of list np >next = pp >next; pp >next = np; cout << " Node " << d << " inserted" << endl; bool LinkedList::SearchNode(int d){ if (head == NULL) return false; // empty list

3 // set up the sentinal at the end of the list ListNode p = head; while (p >data!= d) { delete sp; // note that even though the memory is released, sp is still // pointing at that location so the test below is still ok // return node found or not found if (p!= sp) return true; // found if p is not pointing at the sentinal else return false; void LinkedList::PrintList(){ ListNode ptr = head; cout << "Here's the linked list..." << endl; while(ptr!= NULL){ cout << " " << ptr >data; ptr = ptr >next; cout << endl << endl; if (head == NULL) { cout << "head is pointing to NULL" << endl; cout << "tail is pointing to NULL" << endl; else { cout << "head is pointing to node " << head >data << endl; cout << "tail is pointing to node " << tail >data << endl; bool LinkedList::DeleteNode(int d){ if (head == NULL) { cout << " Did not find " << d << " to delete" << endl; return false; // empty list // search for node to delete // set up the sentinal first. This part is almost the same as the code in the Search routine

4 ListNode p = head; // pointer for traversing the list ListNode pp = p; // previous pointer that follows p while (p >data < d) { pp = p; // update previous pointer delete sp; if (p == sp) { // node not found so no deletion cout << " Did not find " << d << " to delete" << endl; return false; // delete the node where p is pointing at // see where the node is in the list if (p == head) { // delete the head head = p >next; // remove node from the head of the list delete p; // release the memory pointed to by p else if (p == tail) { // delete the tail pp >next = NULL; delete tail; tail = pp; else { // delete the middle pp >next = p >next; delete p; cout << " Node " << d << " deleted" << endl; return true; main.cpp / This program demonstrates the creation of a linked list with a sentinal for search Created by Enoch Hwang on 2/1/10. Copyright 2010 La Sierra University. All rights reserved. / #include <iostream> #include "Linked List.h" using namespace std; void main (int argc, char const argv[]) { LinkedList L; // create an empty list int n, select; while (1) {

5 cout << "1 = insert" << endl; cout << "2 = search" << endl; cout << "3 = delete" << endl; cout << "4 = print list" << endl; cout << "0 = end" << endl; cout << "? "; cin >> select; switch (select) { case 1: cout << "Enter number to insert? "; L.InsertNode(n); case 2: cout << "Enter number to search? "; if(l.searchnode(n) == true) cout << " " << n << " is found in the list" << endl; else cout << " " << n << " is NOT found in the list" << endl; case 3: cout << "Enter number to delete? "; L.DeleteNode(n); case 4: cout << "Linked list..." << endl; L.PrintList(); default: exit (1);