LeetCode：876. 链表的中间结点

876. 链表的中间结点

leetcode-cn.com/problems/mi…

1.双指针 second 比 first 快一倍
2.若整个链表为奇数，在 first = first.next 之前判断 second.next == null，则包含中间的指针

代码：

class Solution {

    public ListNode middleNode(ListNode head) {

        if (head == null) {
            return null;
        }

        ListNode prev = new ListNode(0);
        prev.next = head;

        ListNode first = head;
        ListNode second = head;

        while (second != null ) {
            if (second.next == null) {
                return first;
            }
            first = first.next;
            second = second.next.next;
        }

        return first;
    }
}