力扣876. 链表的中间结点

Problem: 876. 链表的中间结点

题目描述

思路

定义快慢指针fast、slow，fast每次走两步、slow每次一步，当fast指向链表尾节点时，slow指向链表的中间节点

复杂度

时间复杂度:

$O(n)$；其中$n$为单链表的长度

空间复杂度:

$O(1)$

Code

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    /**
     * Middle of the Linked List
     *
     * @param head The head of linked list
     * @return ListNode
     */
    public ListNode middleNode(ListNode head) {
        ListNode fast = head;
        ListNode solw = head;
        while (fast != null && fast.next != null) {
            fast = fast.next.next;
            solw = solw.next;
        }
        return solw;
    }
}