143. 重排链表(Medium)
# 题目描述
给定一个单链表 L:L0→L1→…→Ln-1→Ln , 将其重新排列后变为: L0→Ln→L1→Ln-/1→L2→Ln-2→…
# 样例
Input: 1->2->3->4
Output: 1->4->2->3
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# 解题思路
快慢指针找中点 + 翻转
1->2->3->4->5 # 找中点
1->2->3 4->5 # 切割
1->2->3 5->4 # 随意翻转一个
1->5->2->4->3 # <-- Output
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图解
# 代码
class Solution:
def reorderList(self, head: ListNode) -> None:
def findMiddle(head):
slow, fast = head, head.next
while fast and fast.next:
slow = slow.next
fast = fast.next.next
mid = slow.next
slow.next = None
return mid
def reverse(head):
pre, cur = None, head
while cur:
cur_next_bak = cur.next
cur.next = pre
pre = cur
cur = cur_next_bak
return pre
def mergeTwoList(l1, l2):
dummyHead = ListNode(None)
p = dummyHead
while l1 and l2:
p.next = l1
p = p.next
l1 = l1.next
p.next = l2
p = p.next
l2 = l2.next
p.next = l1 if l1 else l2
return dummyHead.next
if not head or not head.next: return head
l1, l2 = head, findMiddle(head)
l2 = reverse(l2)
return mergeTwoList(l1, l2)
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编辑 (opens new window)
上次更新: 2022/10/25, 02:40:54