1 #include <iostream>
2 using namespace std;
3 struct Listnode//定义链表节点
4 {
5 int val;
6 Listnode* next;
7 Listnode(int _val):val(_val),next(nullptr){}
8 } ;
9 //判断链表是否成环
10 bool cycle(Listnode* head)
11 {
12 Listnode* fast=head;
13 Listnode* slow=head;
14 while(fast!=nullptr && fast->next!=nullptr)
15 {
16 slow=slow->next;
17 fast=fast->next->next;
18 if(slow==fast)
19 {
20
21 return true;
22 }
23 }
24 return false;
25 }
26 //判断链表是否存环，存在返回环开始的节点
27 Listnode* cycle_pos(Listnode* head)
28 {
29 Listnode* slow=head;
30 Listnode* fast=head;
31 while(fast!=nullptr && fast->next!=nullptr)
32 {
33 slow=slow->next;
34 fast=fast->next->next;
35 if(slow==fast)
36 {
37 Listnode* index1=fast;
38 Listnode* index2=head;
39 while(index1!=index2)
40 {
41 index1=index1->next;
42 index2=index2->next;
43 }
44 return index1;
45 }
46 }
47 return nullptr;
48 }
49 int main(int argc, char *argv[])
50 {
51 Listnode* n1=new Listnode(3);
52 Listnode* n2=new Listnode(2);
53 Listnode* n3=new Listnode(0);
54 Listnode* n4=new Listnode(-4);
55 n1->next=n2;
56 n2->next=n3;
57 n3->next=n4;
58 n4->next=n2;
59 cout<<n1->val<<" "<<n2->val<<" "<<n3->val<<" "<<n4->val;
60 bool result=cycle(n1);
61 auto f=[=]{return result?"cycle":"no cycle";};
62 cout<<f()<<endl;//是否成员
63 Listnode* node=cycle_pos(n1);
64 //auto g=[=]{return node?"cycle":"no cycle";};
65 //cout<<g()<<endl;
66 if(node)
67 {
68 cout<<"cycle start is:"<<node->val<<endl;
69 }
70 else{
71 cout<<"no cycle"<<endl;
72 }
73
74 return 0;
75 }
