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51 lines
1.5 KiB
Python
51 lines
1.5 KiB
Python
#!/usr/bin/env python
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# coding=utf-8
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###############################################################################
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# Leetcode 24 两两交换链表中的节点
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#
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# 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。
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# 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。
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###############################################################################
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class ListNode:
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def __init__(self, x):
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self.val = x
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self.next = None
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def __repr__(self):
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if self:
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return "{}->{}".format(self.val, repr(self.next))
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class Solution:
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def swapPairs(self, head):
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"""
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(knowledge)
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思路：
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1. 用三个指针pre(初始为None)，cur(初始为head)，next(初始位head.next)；
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2. 接着借由三个指针完成两个节点的交换
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"""
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if head is None or head.next is None:
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return head
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pre, cur, next, head = None, head, head.next, head.next
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while cur is not None and next is not None:
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if pre is not None:
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pre.next = cur.next
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cur.next, next.next, cur, pre = next.next, cur, next.next, cur
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if cur is not None:
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next = cur.next
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return head
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if __name__ == '__main__':
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solution = Solution()
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head = ListNode(1)
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head.next = ListNode(2)
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head.next.next = ListNode(3)
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head.next.next.next = ListNode(4)
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head.next.next.next.next = ListNode(5)
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print(solution.swapPairs(head))
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