[leetcode]Swap Nodes in Pairs @ Python

原題地址：http://oj.leetcode.com/problems/swap-nodes-in-pairs/

題意：將鏈表中的節點兩兩交換。Given 1->2->3->4, you should return the list as 2->1->4->3.

解題思路：這題主要涉及到鏈表的操作，沒什么特別的技巧，注意不要出錯就好。最好加一個頭結點，操作起來會很方便。

代碼：

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution:
    # @param a ListNode
    # @return a ListNode
    def swapPairs(self, head):
        if head == None or head.next == None:
            return head
        dummy = ListNode(0); dummy.next = head
        p = dummy
        while p.next and p.next.next:
            tmp = p.next.next
            p.next.next = tmp.next
            tmp.next = p.next
            p.next = tmp
            p = p.next.next
        return dummy.next