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LeetCode-24 - Swap Nodes in Pair

LeetCode-24 - Swap Nodes in Pair

作者: 空即是色即是色即是空 | 来源:发表于2017-12-14 19:58 被阅读7次

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. 递归

应该很容易想到用递归来分解计算步骤:

a. 先交换最前面两个元素
b. 再算后面的List
c. 将a/b两步结果接起来

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 not head or not head.next:
            return head
        _head = head.next
        head.next = self.swapPairs(_head.next)
        _head.next = head
        return _head

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