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[刷题] 206 Reverse Linked List

要求

反转一个链表
不得改变节点的值

示例

head->1->2->3->4->5->NULL
NULL<-1<-2<-3<-4<-5<-head

思路

设置三个辅助指针

实现

50实现反转，51-52实现后移

 1 #include <iostream>
 2 using namespace std;
 3 
 4 struct ListNode {
 5     int val;
 6     ListNode *next;
 7     ListNode(int x) : val(x), next(NULL) {}
 8 };
 9 
10 ListNode* createLinkedList(int arr[], int n){
11     if( n == 0 )
12         return NULL;
13     ListNode* head = new ListNode(arr[0]);
14     ListNode* curNode = head;
15     for( int i = 1 ; i < n ; i ++ ){
16         curNode->next = new ListNode(arr[i]);
17         curNode = curNode->next;
18     }
19     return head;
20 }
21 
22 void printLinkedList(ListNode* head){
23     ListNode* curNode = head;
24     while( curNode != NULL ){
25         cout << curNode->val << " -> ";
26         curNode = curNode->next;
27     }
28     cout<<"NULL"<<endl;
29     return;
30 }
31 
32 void deleteLinkedList(ListNode* head){
33     ListNode* curNode = head;
34     while( curNode != NULL){
35         ListNode* delNode = curNode;
36         curNode = curNode->next;
37         delete delNode;
38     }
39     return;
40 }
41 
42 class Solution {
43 public:
44     ListNode* reverseList(ListNode* head) {
45         
46         ListNode* pre = NULL;
47         ListNode* cur = head;
48         while( cur != NULL){
49             ListNode* next = cur->next;    
50             cur->next = pre;
51             pre = cur;
52             cur = next;
53         }
54         return pre;
55     }
56 };
57 
58 int main(){
59     int arr[] = {1,2,3,4,5};
60     int n = sizeof(arr)/sizeof(int);
61     
62     ListNode* head = createLinkedList(arr,n);
63     printLinkedList(head);
64     
65     ListNode* head2 = Solution().reverseList(head);
66     printLinkedList(head2);
67     
68     deleteLinkedList(head2);
69     return 0;
70 }

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