【leetcode】Swap Nodes in Pairs

Swap Nodes in Pairs

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.

注意节点互换的写法：

/**
* Definition for singly-linked list.
* struct ListNode {
*     int val;
*     ListNode *next;
*     ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
ListNode *swapPairs(ListNode *head) {
if(head==NULL || head->next==NULL) return head;
ListNode *temp=head;
ListNode *p1=head;
ListNode *p2;
while(p1!=NULL && p1->next!=NULL)
{
p2=p1->next;//节点互换
p1->next=p2->next;
p2->next=p1;

if(temp!=head)
temp->next=p2;
else
head=p2;

temp=p1;
p1=p1->next;
}
return head;
}
};