Cycle Detection added

Author: neha030

Data Structures/Linked Lists/Detet_Cycle_In_LinkedList.cpp

@@ -0,0 +1,96 @@
+/*
+    A Linked List is a linear data structure which includes a series of connected nodes. 
+    Each node stores the data and the address of the next node.
+    If any node is visited more than once while traversing the list then we can say that it contains cycle/loop.
+     Example:
+                1 -> 2 -> 3
+                    ^     |
+                    |     v
+                    5 <-  4   
+     Output:
+            True
+    Method:In this method we will traverse the linkedlist using two pointers is slow and fast. 
+    Move the slow pointer by one position and fast pointer by two positions.
+    If these two pointers meet together at any point at same node then we can say that there is loop/cycle inside linkedlist. 
+*/
+
+#include <bits/stdc++.h>
+using namespace std;
+
+// Link list node 
+class Node
+{
+public:
+    int data;
+    Node *next;
+};
+
+void push_node(Node **head_ref, int new_data)
+{
+    /* allocate node */
+    Node *new_node = new Node();
+
+    /* put in the data */
+    new_node->data = new_data;
+
+    /* link the old list off the new node */
+    new_node->next = (*head_ref);
+
+    /* move the head to point to the new node */
+    (*head_ref) = new_node;
+}
+
+int detectLoop(Node *list)
+{
+    Node *slow_p = list, *fast_p = list;
+
+    while (slow_p && fast_p && fast_p->next)
+    {
+        slow_p = slow_p->next;
+        fast_p = fast_p->next->next;
+        if (slow_p == fast_p)
+        {
+            return 1;
+        }
+    }
+    return 0;
+}
+
+/* Driver code*/
+int main()
+{
+    /* Start with the empty list */
+    Node *head = NULL;
+    int n = 0;
+    cout << "Enter size of linked list" << endl;
+    cin >> n;
+    int i;
+    int d;
+    cout << "Enter the elements of linked list" << endl;
+    for (int i = 0; i < n; i++)
+    {
+        cin >> d;
+        push_node(&head, d);
+    }
+
+    /* Create a loop for testing */
+    head->next->next->next->next = head;
+    if (detectLoop(head))
+        cout << "True";
+    else
+        cout << "False";
+    return 0;
+}
+
+/*
+ Time complexity: O(n)
+ Space complexity: O(1)
+ 
+ Input :
+ Enter size of linked list
+ 5
+ Enter the elements of linked list
+ 45 24 32 72 54
+ Output :
+ True
+*/