99. Reorder List/143. Reorder List
- 本题难度: Medium
- Topic: Linked List
Description
Given a singly linked list L: L0 → L1 → … → Ln-1 → Ln
reorder it to: L0 → Ln → L1 → Ln-1 → L2 → Ln-2 → …
Example
Given 1->2->3->4->null, reorder it to 1->4->2->3->null.
Challenge
Can you do this in-place without altering the nodes' values?
我的代码
"""
Definition of ListNode
class ListNode(object):
def __init__(self, val, next=None):
self.val = val
self.next = next
"""
class Solution:
"""
@param head: The head of linked list.
@return: nothing
"""
def reorderList(self, head):
# write your code here
def reverse(head):
left = head
right = None
while(left):
tmp = left.next
left.next = right
right = left
left = tmp
return right
def merge(l1,l2):
head1 = l1
head2 = l2
while(l1 and l2):
tmp1 = l1.next
tmp2 = l2.next
l1.next = l2
l2.next = tmp1
l1 = tmp1
l2 = tmp2
return head1
def getmid(head):
slow = head
fast = head.next
while(fast and fast.next):
slow = slow.next
fast = fast.next.next
head2 = slow.next
slow.next = None
return head, head2
if head == None:
return None
l1 ,l2= getmid(head)
l2 = reverse(l2)
head = merge(l1,l2)
思路
分割成两段，后面的翻转，最后插空合并
- 时间复杂度
- 出错