leetcode 24 两两交换链表中的节点

给定一个链表，两两交换其中相邻的节点，并返回交换后的链表。

你不能只是单纯的改变节点内部的值，而是需要实际的进行节点交换。

示例:

给定 1->2->3->4, 你应该返回 2->1->4->3.

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# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class (object):
    def swapPairs(self, head):
        """
        :type head: ListNode
        :rtype: ListNode
        """
        if not head or not head.next:
            return head
        dump = ListNode(-1)
        dump.next = head
        prev = dump
        cur = head
        while cur:
            tail = cur.next
            if not tail:
                break
            cur.next = tail.next
            tail.next = cur
            prev.next = tail
            prev = cur
            cur = cur.next
        return dump.next

• 递归

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  class Solution { public ListNode swapPairs(ListNode head) { if(head == null || head.next == null){ return head; } ListNode next = head.next; head.next = swapPairs(next.next); next.next = head; return next; } }

• 非递归

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  class Solution { public ListNode swapPairs(ListNode head) { ListNode pre = new ListNode(0); pre.next = head; ListNode temp = pre; while(temp.next != null && temp.next.next != null) { ListNode start = temp.next; ListNode end = temp.next.next; temp.next = end; start.next = end.next; end.next = start; temp = start; } return pre.next; } }