[LeetCode] 876. Middle of the Linked List_Easy tag: Linked List ** slow, fast pointers
2018-08-20 09:37 Johnson_强生仔仔 阅读(233) 评论(0) 编辑 收藏 举报Given a non-empty, singly linked list with head node head
, return a middle node of linked list.
If there are two middle nodes, return the second middle node.
Example 1:
Input: [1,2,3,4,5]
Output: Node 3 from this list (Serialization: [3,4,5])
The returned node has value 3. (The judge's serialization of this node is [3,4,5]).
Note that we returned a ListNode object ans, such that:
ans.val = 3, ans.next.val = 4, ans.next.next.val = 5, and ans.next.next.next = NULL.
Example 2:
Input: [1,2,3,4,5,6]
Output: Node 4 from this list (Serialization: [4,5,6])
Since the list has two middle nodes with values 3 and 4, we return the second one.
Note:
- The number of nodes in the given list will be between
1
and100
.
思路直接求出来linked list的长度, 然后再走一半, 返回head即可.
Improve, 可以用slow 和fast 去走, 当fast走到头, 那么slow就在中间了.
Code T: O(n) S: O(1)
# Definition for singly-linked list. # class ListNode: # def __init__(self, x): # self.val = x # self.next = None class Solution: def middleNode(self, head): def helper(head): count = 0 while head: count += 1 head = head.next return count for i in range(helper(head)//2): head = head.next return head