LeetCode 24: 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.

解决思路：更改第二个节点作为表头，定义三个指针，pNode和tNode分别指向交换节点的第一个节点和第二个节点，mNode指向奇数(如1,3,5……)节点。(Time: 4s)

/**
* 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* pNode=head, *tNode=head, *mNode=NULL;
head=pNode->next;
tNode=pNode->next;
while(tNode != NULL)
{
if(mNode) mNode->next=tNode;
pNode->next = tNode->next;
tNode->next=pNode;
tNode=pNode->next;
if(tNode==NULL) break;
mNode=pNode;
pNode=tNode;
tNode = pNode->next;
}
return head;
}
};