编程练习 链表题目反序，合并

Code Snippet

1. #include <iostream>
2. #include<fstream>
3.  
4. using namespace std;
5.  
6. struct Node
7. {
8.         int data ;
9.         Node *next ;
10. };
11. typedef struct Node Node ;
12.  
13. void ReverseList(Node*& head)
14. {
15.     if(head == NULL || head->next == NULL)
16.         return;
17.  
18.     Node* currentNode = head;
19.     Node* previousNode = NULL;
20.  
21.     while(currentNode != NULL)
22.         ...{
23.             Node* temp = currentNode->next;
24.             currentNode->next = previousNode;
25.             previousNode = currentNode;
26.             currentNode = temp;
27.     }
28.  
29.     head = previousNode;
30. }
31.  
32. // My answer.
33. Node* MergeLinkList(Node* listA, Node* listB)
34. {
35.     if(listA == NULL)
36.         return listB;
37.     if(listB == NULL)
38.         return listA;
39.  
40.     Node* pHeadSmall = listA -> data < listB -> data ? listA : listB;
41.     Node* pHeadBig = pHeadSmall == listA ? listB : listA;
42.  
43.     Node* p = pHeadSmall;
44.     Node* q = pHeadSmall->next;
45.     Node* r = pHeadBig;
46.  
47.     while(q != NULL && r != NULL)
48.         ...{
49.             if(q->data <= r->data)
50.                 ...{
51.                     p->next = q;
52.                     p = p->next;
53.                     q = q->next;
54.             }
55.             else
56.                 ...{
57.                     p->next = r;
58.                     p = p->next;
59.                     r = r->next;
60.             }
61.     }
62.     if(q == NULL)
63.     {
64.             p->next = r;
65.     }
66.     else
67.     {
68.             p->next = q;
69.     }
70.     return pHeadSmall;
71. }
72.  
73. // Standard answer
74. Node * Merge(Node *head1 , Node *head2)
75. {
76.     if ( head1 == NULL)
77.         return head2 ;
78.     if ( head2 == NULL)
79.         return head1 ;
80.     Node *head = NULL ;
81.     Node *p1 = NULL;
82.     Node *p2 = NULL;
83.     if ( head1->data < head2->data )
84.     {
85.             head = head1 ;
86.             p1 = head1->next;
87.             p2 = head2 ;
88.     }
89.     else
90.     {
91.             head = head2 ;
92.             p2 = head2->next ;
93.             p1 = head1 ;
94.     }
95.     Node *pcurrent = head ;
96.     while ( p1 != NULL && p2 != NULL)
97.     {
98.             if ( p1->data <= p2->data )
99.             {
100.                     pcurrent->next = p1 ;
101.                     pcurrent = p1 ;
102.                     p1 = p1->next ;
103.             }
104.             else
105.             {
106.                     pcurrent->next = p2 ;
107.                     pcurrent = p2 ;
108.                     p2 = p2->next ;
109.             }
110.     }
111.     if ( p1 != NULL )
112.         pcurrent->next = p1 ;
113.     if ( p2 != NULL )
114.         pcurrent->next = p2 ;
115.     return head ;
116. }
117.  
118. // Utillity function.
119. void TestList(Node* head)
120. {
121.     Node* p = head;
122.     while(p != NULL)
123.     {
124.             cout << p->data << endl;;
125.             p= p->next;
126.     }
127. }
128.  
129. // Utillity function.
130. Node* InputList(ifstream& inFile)
131. {
132.     int len;
133.     inFile >> len;
134.     Node* head = new Node[len];
135.     Node* p = head;
136.     for(int i = 0; i < len - 1; i++)...{
137.         inFile >> p->data;
138.         p->next = p + 1;
139.         p = p->next;
140.     }
141.     inFile >> p->data;
142.     p->next = NULL;
143.  
144.     return head;
145. }
146.  
147. int main()
148. {
149.     ifstream inFile("d:\data.txt");
150.     if(!inFile)
151.         return -1;
152.  
153.     Node* headA = InputList(inFile);
154.     Node* headB = InputList(inFile);
155.  
156.     TestList(headA);
157.     TestList(headB);
158.  
159.     ReverseList(headA);
160.     cout<< "Testing Reverse A" << endl;
161.     TestList(headA);
162.  
163.     ReverseList(headA);
164.     cout<< "Testing Reverse A back." << endl;
165.     TestList(headA);
166.  
167.     Node* newHead = Merge(headA, headB);
168.     cout<< "Testing Merged List." << endl;
169.     TestList(newHead);
170.  
171.     while(newHead != NULL)
172.     {
173.         Node* ptr = newHead;
174.         newHead = newHead->next;
175.         delete ptr;
176.     }
177. }