876.Middle of the Linked List

tags: Easy,Linked List,Two Pointers

876. Middle of the Linked List

題目描述

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.

範例

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

解答

Python

# 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]:
        slow = fast = head
        
        while fast and fast.next:
            slow, fast = slow.next, fast.next.next
            
        return slow

Kobe Dec 5, 2022

Javascript

function middleNode(head) {
  let slow = head;
  let fast = head;
  while (fast && fast.next) {
    slow = slow.next;
    fast = fast.next.next;
  }

  return slow;
}

Marsgoat Dec 5, 2022

C#

public class Solution {
    public ListNode MiddleNode(ListNode head) {
        var slow = head;
        var fast = head;
        
        while (fast.next != null) {
            slow = slow.next;
            fast = fast.next;
            
            if (fast.next == null) break;
                
            fast = fast = fast.next;
        }
        
        return slow;
    }
}

Jim Dec 5, 2022

Reference

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