0876. Middle of the Linked List #

题目 #

给定一个头结点为head的非空单链表，返回链表的中间结点。
如果有两个中间结点，则返回第二个中间结点。

思路 #

双指针 #

代码 #

双指针 #

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 {
    public ListNode middleNode(ListNode head) {
        ListNode sentinel = new ListNode(-1, head);
        ListNode middle = sentinel, fast = sentinel;
        while (fast != null && fast.next != null) {
            middle = middle.next;
            fast = fast.next.next;
        }
        if (fast != null) middle = middle.next;
        return middle;
    }
}