876. Middle of the Linked List

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.

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给定一个单向链表，要求找到其中间节点。

简单题，快慢指针，快指针的速度是慢指针的2倍，则当快指针走到末尾时，慢指针正好指向中间位置。代码如下：

class Solution {
public:
	ListNode* middleNode(ListNode* head) {
		if (head == NULL || head->next == NULL)return head;
		ListNode *fast = head, *slow = head;
		while (fast->next) {
			fast = fast->next->next;
			slow = slow->next;
			if (fast == NULL)break;
		}
		return slow;
	}
};

本代码提交AC，用时0MS。