剑指offer 有环链表

#include <iostream>
#include <string>
#include <vector>
#include <stack>
using namespace std;

typedef int datatype;

struct Node
{
datatype value;
Node* Next_Node;
};

struct Node_circle
{
unsigned int Number;
Node *entrace;
};

//判断链表中是否有环
Node* Exist_circle(Node *first)
{

if (first == nullptr || first->Next_Node == nullptr)
{
return nullptr;
}

Node* Node_temp1 = first->Next_Node;
Node* Node_temp2 = Node_temp1->Next_Node;

while (Node_temp2 != nullptr && Node_temp1 != nullptr)
{

Node_temp1 = Node_temp1->Next_Node;
Node_temp2 = Node_temp2->Next_Node;
//在链表中，每一个节点为nullptr时是否影响到程序的鲁棒性，造成程序崩溃，都必须考虑在内
if (Node_temp2->Next_Node != nullptr)
{
Node_temp2 = Node_temp2->Next_Node;
}

if (Node_temp1 == Node_temp2)
{
return Node_temp1;
break;
}
}
return nullptr;
}

//输出环中结点的个数以及环的入口
Node_circle* Find_circle(Node *first)
{
Node* Node_temp5 = Exist_circle(first);
if (Node_temp5 == nullptr)
{
return nullptr;
}

int number = 1;
//已存在环,无需判断下一个节点是否为nullptr了
Node* Node_temp3 = Node_temp5->Next_Node;
while (Node_temp3 != Node_temp5)
{
Node_temp3 = Node_temp3->Next_Node;
number++;
}

Node* entrace = first;
for (int i = 0;i<number;i++)
{
entrace = entrace->Next_Node;
}

Node* Node_temp4 = first;
while (Node_temp4 != entrace)
{
Node_temp4 = Node_temp4->Next_Node;
entrace = entrace->Next_Node;
}

Node_circle* circle_Node;
circle_Node->Number = number;
circle_Node->entrace = entrace;

return circle_Node;
}

void main()
{

system("pause");
}