[LeetCode] 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.

相关问题：[LeetCode] Reverse Nodes in k-Group

代码：

/** * 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) {                ListNode* current = head;          ListNode* next = NULL;          ListNode* prev = NULL;                  if(current)        {            next = current->next;            current->next = prev;            prev = current;            current = next;        }                if(current)        {            next = current->next;            current->next = prev;            prev = current;            current = next;        }                if(next)            head->next = swapPairs(next);                return prev;    }};