Method1: Detect and remove loop in a linked list

1. detect loop

2. store the address of the common node in a pointer

3. put slow pointer on head

4. move both pointers by unit 1

5. Now make the next of the common node found again point to null.

Detect loop using Floyd cycle detection algorithm and then 

#include <iostream>

#include <bits/stdc++.h>

using namespace std;

struct node{

    int data;

    struct node* next;

};

void remloop(struct node*, struct node*);

int detandremloop(struct node* list)

{

    struct node *sp=list, *fp=list;

    while(sp&& fp&& fp->next)

    {

        sp= sp->next;

        fp= fp->next->next;

        if(sp==fp) {

            remloop(sp, list);

            return 1;

        } //if ends

        

    } //while loop ends

   return 0; 

} //int ends

void remloop(struct node* loop_node , struct node* head)

{

    struct node *ptr1;

    struct node *ptr2;

    ptr1= head;

    while(1)

    {

        ptr2 = loop_node;

        while(ptr2->next !=loop_node && ptr2->next != ptr1)

        ptr2= ptr2->next;

        if(ptr2->next==ptr1) break;

        ptr1=ptr1->next;

    } //while loop ends

        ptr2->next= NULL;

    

} //f ends

void printlist(struct node* node)

{

    while(node!= NULL){

    cout<<node->data<< " ";

    node=node->next;} //while ends

} //f ends

struct node* newnode(int key)

{

    struct node* temp= new node();

    temp->data= key;

    temp->next= NULL;

    return temp;

    

} //newnode ends

int main() {

struct node* head = newnode(50);

head->next= newnode(20);

head->next->next= newnode(15);

head->next->next->next= newnode(4);

head->next->next->next->next= newnode(10);

head->next->next->next->next->next= head->next->next;

detandremloop(head);

printlist(head);

return 0;

}