Leetcode Swap Nodes in Pairs

1. Topics

Given a linked list, swap every, 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. Modify the values in the list, only nodes itself can be changed.

2. Solution

Class Solution {public:       listnode *swappairs (ListNode *head) {       listnode* returnnode  = head; listnode* Prenode = Null;while (head! = NULL && Head->next! = null) {listnode* firstnode = head; listnode* Secondnode = head->next;if (prenode! = NULL) {//first nodeprenode->next = Secondnode;} Else{if (Secondnode! = NULL) {returnnode = Secondnode;}} Firstnode->next = Secondnode->next;secondnode->next = Firstnode;prenode = Head;head = Head->next;} return returnnode;}    ;

idea: This question is still relatively simple. While loop, swapping two pointers. But pay attention to the details and the values returned.

http://www.waitingfy.com/archives/1583

Leetcode Swap Nodes in Pairs