链表的中间结点

 

链表的结点为空时无法访问其next成员否则会报错

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     struct ListNode *next;
 * };
 */

typedef struct ListNode ListNode;
struct ListNode* middleNode(struct ListNode* head){
    if(head==NULL){
        return NULL;
    }
    ListNode*slow,*fast;
    fast=slow=head;
    while(fast&&fast->next){
        slow=slow->next;
        fast=fast->next->next;
    }
return slow;
}