求链表中间结点

#include <stdio.h>
#include <stdlib.h>
/*
查找链表中间的结点。
思路1：求长度：中间结点 = len/2
思路2：定义两个指针p1,p2指向头结点，p1走一步，p2走两步，当p2指向尾结点的下一个结点的时候，p1指向中间结点。
       疑问：比如链表有5个结点，那么第3个是中间结点毫无疑问，但是如果6个结点，那么第3个算中间结点，还是第4个算中间结点呢？
*/
typedef struct node
 {
     int data;
      struct node * next;
 }NODE;
 NODE * createList()
{
     NODE * head = (NODE *)malloc(sizeof(NODE));
     head->next = NULL;
 
     return head;
 }
 void insertNode(NODE *head,int insertData)
 {
     NODE * sur = (NODE *)malloc(sizeof(NODE));
     sur->data = insertData;

     sur->next = head->next;
     head->next = sur;
 
 }
 void traverList(NODE *head)
 {
     int i = 1;
     head = head->next;
     while(head)
     {
         printf("第%d结点 = %d\n",i,head->data);
        head = head->next;
         i++;
    }
 }
 NODE *middleList(NODE *head)
 {
     NODE *p1,*p2;
     p1 = p2 = head;
     while(p2)
     {
        p1 = p1->next;
        p2 = p2->next;
        if(p2 !=NULL)
            p2 = p2->next;

     }
     return p1;
 }
 int main(void)
 {
     NODE *head = createList();
     for(int i = 0;i<5;i++)
         insertNode(head,rand()%100);
     traverList(head);
     NODE * p1 = middleList(head);
     printf("中间结点数据 = %d\n",p1->data);
     return 0;
 }