[Re] Added Detecting and Removing Cycle from a linked list (jainaman224#1047)

Author: saumyashrm2802

Linked_List/Cycle_Detection_Removal.cpp

@@ -0,0 +1,108 @@
+/*
+Technique used:
+
+This method of detecting cycle is dependent upon Floyd's Cycle Detection Algorithm.
+In Floyd's Cycle Detection Algorithm, we take two pointers : fast and slow.
+The algorithm comes to an end when both of these pointers meet at a common point.
+Then, we store the address of the common point in a pointer variable (temp here).
+We start form the head of the linked list, and check each node if it is reachable
+from temp. That particular node, if found, is the starting node of the linked list.
+We assign a pointer to the previous one of this node.
+*/
+
+#include<iostream>
+using namespace std;
+
+struct node
+{
+    int info;
+    node *next;
+};
+
+//creating a new node
+node *create (int x) 
+{
+    node *ptr = new node;
+    ptr->info = x;
+    ptr->next = NULL;
+    return ptr;
+}
+
+//printing the linked list
+void print (node * ptr) 
+{
+    while (ptr != NULL)
+    {
+        cout << ptr->info << " ";
+        ptr = ptr->next;
+    }
+    cout << "\n\n";
+}
+
+//removing the cycle from the linked list
+void rem (node * slow_ptr, node * head) 
+{
+    node *ptr;
+    node *temp;
+    ptr = head;
+    while (1)
+    {
+        temp = slow_ptr;
+        while (temp->next != slow_ptr && temp->next != ptr)
+            {
+                temp = temp->next;
+            }
+            if (temp->next == ptr)
+                break;
+            ptr = ptr->next;
+    }
+    temp->next = NULL;
+}
+
+//detecting cycle in the linked list
+int detect (node * ptr) 
+{
+    node *slow_ptr = ptr;
+    node *fast_ptr = ptr;
+    while (slow_ptr && fast_ptr && fast_ptr->next)
+    {
+        slow_ptr = slow_ptr->next;
+        fast_ptr = fast_ptr->next->next;
+        if (slow_ptr == fast_ptr)
+        {
+            //remove function called
+            rem (slow_ptr, ptr); 
+            return 1;
+        }
+    }
+    return 0;
+}
+
+int main ()
+{
+    node *head = create (10);
+    head->next = create (20);
+    head->next->next = create (30);
+    head->next->next->next = head;
+    //detect function called
+    if (detect (head) == 1) 
+    {
+        cout << "\nA cycle is present in the linked list\n";
+        cout << "\n\nAfter removing the cycle, linked list is as follows:\n";
+        //print function called
+        print (head); 
+    }
+    else
+        cout << "No cycle is present within the loop\n";
+    return 0;
+}
+
+/* Sample input :HARDCORED VALUES:
+    10->20->30->(attached to head)
+
+     Sample output:
+     A cycle is present in the linked list
+
+     After removing the cycle, linked list is as follows:
+     10 20 30
+/*