题目:
Given a linked list, swap every two adjacent nodes and return its head.
For example,
Given 1->2->3->4, you should return the list as 2->1->4->3.
Your algorithm should use only constant space. You may not modify the values in the list, only nodes itself can be changed.
代码:
1 class Solution{ 2 public: 3 void swap(ListNode *node1,ListNode *node2){ 4 node1->next=node2->next; 5 node2->next=node1; 6 } 7 8 ListNode* swapPairs(ListNode *head){ 9 if(head==NULL || head->next==NULL) return head; 10 ListNode *ppre=NULL,*pre=NULL; 11 ListNode *tmp=NULL; 12 ListNode *p=head; 13 14 while(p){ 15 pre=p; 16 p=p->next; 17 if(p->next){ 18 tmp=p->next; 19 } 20 21 if(pre==head) head=p; 22 if(ppre) ppre->next=p; 23 24 ppre=pre; 25 p=tmp; 26 } 27 return head; 28 } 29 };
原文：http://www.cnblogs.com/sixue/p/4011605.html