LeetCode 876. Middle of the Linked List（获得链表中心结点）

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* middleNode(ListNode* head) {
        if(head == NULL || head -> next == NULL) return head;
        ListNode *fast = head;
        ListNode *slow = head;
        while(fast && fast -> next){
            fast = fast -> next -> next;
            slow = slow -> next;
        }
        return slow;
    }
};