Posted on 2022-12-06 15:55
Uriel 阅读(51)
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数据结构 、
闲来无事重切Leet Code
给一个单链表,要求重新排序,前一半为链表的奇数位,后一半为偶数位,e.g.,
Input: head = [1,2,3,4,5]
Output: [1,3,5,2,4]
设置三个指针位置,odd表示当前奇数位处理到哪里,r表示目前已处理到的位置的下一位,even表示当前偶数位处理到哪里,另设置pos记录当前已经处理过多少个(用于判断奇偶)
1.如果当前处理偶数位,odd指向r,r指向next,even不变,e.g.,
1->3->2->4->5->6->7 (此时odd指向3,even指向2,r指向4)
在处理节点4时,指针更新为:odd依旧指向3,even指向4,r指向5,链表顺序不变
2.如果当前处理奇数位,先用临时变量记录第一个偶数位(first_even = odd.next),r的下一位(r_next = r.next),然后分五步改变链表指针顺序
1->3->2->4->5->6->7 (此时odd指向3,even指向4,r指向5)
s1:更新odd.next = r (让3的下一位指向5)
s2:更新r.next = first_even (让5的下一位指向2)
s3:更新even.next = r_next (让4的下一位指向6)
s4:更新odd = r (此时odd指向5)
s5:更新r = r_next (此时r指向6)
更新后链表顺序为:1->3->5->2->4->6->7 (此时odd指向5,even指向4,r指向6)
复杂度O(n),内存O(1)
1 #328
2 #Runtime: 73 ms
3 #Memory: 17.1 MB
4
5 # Definition for singly-linked list.
6 # class ListNode(object):
7 # def __init__(self, val=0, next=None):
8 # self.val = val
9 # self.next = next
10 class Solution(object):
11 def oddEvenList(self, head):
12 """
13 :type head: ListNode
14 :rtype: ListNode
15 """
16 if not head:
17 return head
18 pos = 1
19 r = head.next
20 odd = head
21 even = head
22 while r:
23 if pos % 2:
24 even = r
25 r = r.next
26 else:
27 first_even = odd.next
28 r_next = r.next
29 odd.next = r
30 r.next = first_even
31 even.next = r_next
32 odd = r
33 r = r_next
34 pos += 1
35 return head