011_hasCycle

 /*
  * Author ：SJQ
  *
  * Time   ：2014-07-16-20.21
  *
  */
 #include <iostream>
 #include <cstdio>
 #include <cstdlib>
 using namespace std;

 struct ListNode {
 int val;
 ListNode *next;
 ListNode(int x) : val(x), next(NULL) {}
 };

 //利用快慢指针，链表有环，则快慢指针一定会相遇
 bool hasCycle(ListNode *head)
 {
     if (!head|| !head->next)
 return false;

     ListNode *fast, *slow;
     fast = slow = head;
     while(fast)
     {
         if (!fast->next)
 return false;

         fast = fast->next->next;
         slow = slow->next;

         if (fast == slow)
         {
             return true;
         }
     }

     return false;
 }

 int main()
 {
     freopen("input.txt", "r", stdin);
 int n;
 ListNode *head, *tail;

 while(cin >>n)
 {
 int num;
 for (int i = ; i < n; ++i)
 {
 cin >> num;
 ListNode *temp = (ListNode*)malloc(sizeof(ListNode));
 temp->val = num;
 temp->next = NULL;

 if (i == )
 {
 head = temp;
 tail = temp;
 }
 else
 {
 tail->next = temp;
 tail = tail->next;
 }

 tail->next = NULL;
 }

         tail->next = head->next;        //手动每次把最后一个节点和第二个节点连起来
 bool flag = hasCycle(head);
         if (flag)
             cout << "has cycle!" << endl;
         else
             cout << "no cycle!" << endl;
 tail = head;
 for (int i = ; i < n; ++i)

 {
    cout << tail->val << " ";
 tail =tail->next;
 }
 cout << endl;
 }

 return ;

 }