【LEETCODE】24-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.

题意：

给一个linked list，每两个元素进行互换，最后返回head

算法只能用常数空间，不可以修正list中的值，只能交换节点

参考：

http://www.cnblogs.com/zuoyuan/p/3701919.html

Python

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

class Solution(object):
    def swapPairs(self, head):
        """
        :type head: ListNode
        :rtype: ListNode
        """
        
        if head is None or head.next is None:
            return head
        
        dum=ListNode(0)
        dum.next=head
        
        p=dum
        
        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 dum.next