[Leetcode] swap nodes in pairs

Given a linked list, swap every two adjacent nodes and return its head.

For example,
Given1->2->3->4, You shoshould return the list2->1->4->3.

Your algorithm shocould use only constant space. You may not modify the values in the list, only nodes itself can be changed.

 

 1 /** 2  * Definition for singly-linked list. 3  * struct ListNode { 4  *     int val; 5  *     ListNode *next; 6  *     ListNode(int x) : val(x), next(NULL) {} 7  * }; 8  */ 9 class Solution {10 public:11     ListNode *swapPairs(ListNode *head) {12         if (head == NULL || head->next == NULL) return head;13         14         ListNode **prev = &head;15         while ((*prev) != NULL && ((*prev)->next) != NULL) {16             ListNode *pcurr = *prev;17             ListNode *pnext = (*prev)->next;18             pcurr->next = pnext->next;19             pnext->next = pcurr;20             *prev = pnext;21             prev = &(pcurr->next);22         }23             24         return head;25     }26 };

 

[Leetcode] swap nodes in pairs