题目
Given the head
of a singly linked list, return the middle node of the linked list.
If there are two middle nodes, return the second middle node.
Example 1:
Input: head = [1,2,3,4,5]
Output: [3,4,5]
Explanation: The middle node of the list is node 3.
Example 2:
Input: head = [1,2,3,4,5,6]
Output: [4,5,6]
Explanation: Since the list has two middle nodes with values 3 and 4, we return the second one.
Constraints:
- The number of nodes in the list is in the range
[1, 100]
. 1 <= Node.val <= 100
思路
快慢指针,双指针同时前进,快指针步进两步,满指针步进一步,等到快指针步进至链表尾部时,满指针就在链表的中间。
代码
python版本:
# Definition for singly-linked list.
# class ListNode:
# def __init__(self, val=0, next=None):
# self.val = val
# self.next = next
class Solution:
def middleNode(self, head: Optional[ListNode]) -> Optional[ListNode]:
l=r=head
while r and r.next:
l=l.next
r=r.next.next
return l