Swap Nodes in Pairs--leetcode

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.

Idea: Split the list and then merge

List *swappairs (list *head) {    if (head = = NULL | | head->next = = NULL)     return head;    list* Ji=head;    list* OU = head->next;    list* TEMP1,*TEMP2;    list* l1= head;    list* L2 = head->next;    Temp1 = l2->next;    while (Temp1! = NULL)    {      Temp2 = temp1->next;      L1->next = Temp1;      L2->next = Temp2;      L1 = Temp1;      L2 = Temp2;      if (L2!=null)      Temp1 = l2->next;      else      temp1 = NULL;    }    if (L1! = NULL)    l1->next =null;    if (L2! = null)    l2->next = null;    Temp1 = ou;    while (Temp1! = null&&temp1->next! = NULL)    {        Temp2 = ji->next;       Ji->next = temp1->next;       Temp1->next = Ji;       Temp1 = ji->next;       Ji = temp2;             }    Temp1->next = Ji;    

Swap Nodes in Pairs--leetcode