共计 1065 个字符，预计需要花费 3 分钟才能阅读完成。
题目
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 and 100.
题目地址
讲解
一看到这个题目我就知道用快慢指针。但具体操作的时候有些细节需要注意，要让快慢指针指向第 0 个位置，而不是 head（head 算作第一个位置）。
Java 代码
/**
* Definition for singly-linked list.
* public class ListNode {
* int val;
* ListNode next;
* ListNode(int x) {val = x;}
* }
*/
class Solution {
public ListNode middleNode(ListNode head) {
System.out.println(head.val);
ListNode slow = new ListNode(0);
ListNode fast = new ListNode(0);
slow.next = head;
fast.next = head;
while(slow!=null && fast!=null){
slow = slow.next;
if(fast.next!=null){
fast = fast.next.next;
}else{
fast = fast.next;
}
}
return slow;
}
}
