qiaoxu123
11/19/2018 - 11:57 PM

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.
test1.cpp
content_copyfile_download
//自己的思路：首先遍历一遍进行计数，然后直接访问到中值即可

/**
 * 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) {
        ListNode* p = head;
        ListNode* q = head;
        int num = 0;
        while(p->next != NULL){
            p = p->next;
            num++;
        }
        
        num += 1;
        
        num /= 2;
        
        while(num > 0){
            q = q->next;
            num--;
        }
        return q;
    }
};
test2.cpp
content_copyfile_download
//大神思路，使用快慢指针同时进行
class Solution {
public:
    ListNode* middleNode(ListNode* head) {
        ListNode *slow = head, *fast = head;
        while (fast && fast->next)
            slow = slow->next, fast = fast->next->next;
        return slow;
    }
};