Practice Notes 9 — System & Data Structure

Chpater 9 System, Data Structure

1. LeetCode 24 Swap Nodes in Pairs

   Problem:

   Given a linked list, swap every two adjacent nodes and return its head.

   You may not modify the values in the list's nodes, only nodes itself may be changed.

   Example:

   Given 1->2->3->4, you should return the list as 2->1->4->3.
   

   Solution: 解决这类问题一定要把链表的连接顺序画出来，同时注意边界条件！

   # Definition for singly-linked list.
   # class ListNode:
   #     def __init__(self, val=0, next=None):
   #         self.val = val
   #         self.next = next
   class Solution:
       def swapPairs(self, head: ListNode) -> ListNode:
           dummy = ListNode(None, head)
           prev = dummy
           while head and head.next:
               # first and second
               first = head
               second = head.next
               # Swap
               # prev 接second
               # first 接second 下面一个
               # second 接 first
               # 完成
               prev.next = second
               first.next = second.next
               second.next = first
               # 更新prev， prev指向swap后的first
               # head变成swap后的first的下一个
               prev = first
               head =first.next
               
           return dummy.next

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