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.

Solution: 1. Iterative solution with constant space.
2. Recursive solution with O(n) space (for practice).

 1 class Solution {
 2 public:
 3     ListNode *swapPairs(ListNode *head) {
 4         ListNode dummy(0);
 5         ListNode* cur = &dummy;
 6         cur->next = head;
 7         while(cur->next && cur->next->next) {
 8             ListNode* move = cur->next->next;
 9             cur->next->next = move->next;
10             move->next = cur->next;
11             cur->next = move;
12             cur = move->next;
13         }
14         return dummy.next;
15     }
16 };