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 = 0; i < n; ++i)
{
cin >> num;
ListNode *temp = (ListNode*)malloc(sizeof(ListNode));
temp->val = num;
temp->next = NULL;

if (i == 0)
{
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 = 0; i < n; ++i)

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

return 0;

}