Merge pull request #197 from Upanishadkachroo/detect-cycle-linkedlist

Add detect_cycle_in_linked_list.cpp using Hare and Tortoise algorithm

Author: admirerr

CPP/linked-list/detect_cycle_in_linked_list.cpp

@@ -0,0 +1,108 @@
+/*
+Problem: Detect Cycle in a Linked List
+
+Description:
+This program detects if a singly linked list contains a cycle (loop) using
+Floyd's Hare and Tortoise algorithm. The algorithm uses two pointers moving 
+at different speeds. If there is a loop, the two pointers will meet.
+*/
+
+#include<bits/stdc++.h>
+using namespace std;
+
+class Node{
+    public:
+    int data;
+    Node* next;
+
+    Node(int val){
+        data = val;
+        next = NULL;
+    }
+};
+
+class LinkedList{
+    private:
+    Node* head;
+
+    public:
+    LinkedList(){
+        head = NULL;
+    }
+
+    void insertatend(int val){
+        Node* newNode = new Node(val);
+        if(head == NULL){
+            head = newNode;
+            return;
+        }
+        Node* temp = head;
+        while(temp->next != NULL){
+            temp = temp->next;
+        }
+        temp->next = newNode;
+    }
+
+    void createloop(int pos){
+        if(pos <= 0) return;
+        Node* temp = head;
+        Node* loopnode = nullptr;
+        int count = 1;
+
+        while (temp->next) {
+            if (count == pos) loopnode = temp;
+            temp = temp->next;
+            count++;
+        }
+        temp->next = loopnode; 
+    }
+
+    bool hascycle(){
+        Node* slow = head;
+        Node* fast = head;
+
+        while(fast != NULL && fast->next != NULL){
+            slow = slow->next;
+            fast = fast->next->next;
+
+            if(slow == fast){
+                return true;
+            }
+        }
+        return false;
+    }
+
+    void display(){
+        Node* temp = head;
+        while(temp != NULL){
+            cout << temp->data << " -> ";
+            temp = temp->next;
+        }
+        cout << "NULL" << endl;
+    }
+
+
+};
+
+int main(){
+    LinkedList ll;
+
+    ll.insertatend(1);
+    ll.insertatend(2);
+    ll.insertatend(3);
+    ll.insertatend(4);
+    ll.insertatend(5);
+    ll.insertatend(6);
+    ll.insertatend(7);
+
+    cout<<"Linked List: ";
+    ll.display();
+
+    ll.createloop(3);
+
+    if(ll.hascycle()){
+        cout<<"Cycle detected in the linked list"<<endl;
+    } else {
+        cout<<"No cycle detected in the linked list"<<endl;
+    }
+}