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Loop_in_Linked_List_2.cpp
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Loop_in_Linked_List_2.cpp
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//{ Driver Code Starts
//Initial template code for C++
#include <bits/stdc++.h>
using namespace std;
struct Node
{
int data;
Node* next;
Node(int val)
{
data = val;
next = NULL;
}
};
void loopHere(Node* head, Node* tail, int position)
{
if(position==0) return;
Node* walk = head;
for(int i=1; i<position; i++)
walk = walk->next;
tail->next = walk;
}
// } Driver Code Ends
//User function template for C++
// https://leetcode.com/problems/linked-list-cycle-ii/
// Detect Loop in Linked List and return head
// Given a linked list of N nodes.
// The task is to check,
// if the linked list has a loop and return the starting point of loop.
// Linked list can contain self loop.
/*
struct Node
{
int data;
struct Node *next;
Node(int x) {
data = x;
next = NULL;
}
*/
class Solution
{
public:
//Function to check if the linked list has a loop.
Node* detectLoop_and_return_head(Node* head)
{
Node *slow=head,*fast=head;
while(fast && fast->next){
slow=slow->next;
fast=fast->next->next;
if(slow==fast)
{
Node *cur=head;
while(cur!=slow){
slow=slow->next;
cur=cur->next;
}
return slow;
}
}
return NULL;
}
};
//{ Driver Code Starts.
int main()
{
int t;
cin>>t;
while(t--)
{
int n, num;
cin>>n;
Node *head, *tail;
cin>> num;
head = tail = new Node(num);
for(int i=0 ; i<n-1 ; i++)
{
cin>> num;
tail->next = new Node(num);
tail = tail->next;
}
int pos;
cin>> pos;
loopHere(head,tail,pos);
Solution ob;
Node *temp=ob.detectLoop_and_return_head(head);
if(temp)
cout<<temp->data<<"\n";
else
cout<<"False\n";
}
return 0;
}
// } Driver Code Ends