Given a singly linked list, find if there exist a loop.

Given a singly linked list, find if there exist a loop.

Solution:

#include "stdafx.h"
#include <iostream>
using namespace std;

class Node
{
public:
	void addNode(Node* node);
	void loopStart();
	void loopEnd();
	void setVal(int val) {this->val = val;}
	int getVal() {return this->val;}
	Node(int val) {this->val = val;}
	bool isLoopExist();
	void setN();

	Node* start_end_node;
	int val;
	Node* next;
	Node* end;
	int n;

};
void Node::addNode(Node* node)
{
	if(end == NULL)
		*end = Node(0);
	else
	{
		end->next = node;
		end = end->next;
	}
}

void Node::loopStart()
{
	start_end_node = end;
}
void Node::loopEnd()
{
	end->next = start_end_node;
}
bool Node::isLoopExist()
{
	if(this && this->next)
	{
		Node* first =  this;
		Node* second = this;
		while(first != second)
		{
			first =  first->next;
			second = second->next->next; 
		}
		
		return true;
	
	}
		return false;

}


int _tmain(int argc, _TCHAR* argv[])
{
	Node* head = new  Node(0);
	head->end = head;
	Node* head_next = head;
	int i = 0;


	for(i=1; i<10; ++i)
	{
		Node* temp = new Node(i);
		head->addNode(temp);
	}
	head->loopStart();

	int j = 0;
	for(j=10; j<20; ++j)
	{
		Node* temp = new Node(j); //if we define objects here, then the stack gonna automatic delete itself
					  // 以后遇到链表问题不用多想，一律用指针
		head->addNode(temp);
	}
	head->loopEnd();
	if(head->isLoopExist())
	{
		cout << "a loop exist" << endl;
	}
	else
	{
		cout << "no loop exist" << endl;
	}
	return 0;
}