Question

Using Python Create a simple linked list by defining a struct (in C/C++) or a class (in Python3). For example, in C/C++:
struct singly_linked_list
{
int data;
singly_linked_list *next;
};

(Make sure you understand the concept of pointers - or lack thereof - in Python.)

Write a function to determine if there is a cycle in the singly linked list. Return 1 if there is a cycle in the list, 0 if no cycle. This is a very common interview question. Think carefully about how to solve this. There are myriad solutions online which you should not consult

Answer 1

#CODE IN PYTHON
class Node:
    def __init__(self, val = None):
        self.data = val
        self.next = None

class LinkedList:
    def __init__(self):
        self.head = None
        self.tail = None

    def insert(self, val):
        if self.head == None:
            self.head = Node(val)
            self.tail = self.head
        else:
            self.tail.next = Node(val)
            self.tail = self.tail.next

    def print(self):
        ptr = self.head
        while ptr is not None:
            print(ptr.data, end = " ")
            ptr = ptr.next
        print()

    def isCycle(self):
        slowPtr = self.head# This will move one node at a time
        fastPtr = self.head# This will move two nodes at a time

        while slowPtr != None and fastPtr.next != None:
            slowPtr = slowPtr.next # Move past one node
            fastPtr = fastPtr.next.next # Move past two nodes
            if slowPtr == fastPtr: # If at any point of time both of them points to same node
                return 1 # Cycle is present
        return 0 # Cycle is not present

ll = LinkedList()
ll.insert("Monday")
ll.insert("Tuesday")
ll.insert("Wednesday")
ll.insert("Thursday")
ll.insert("Friday")
ll.insert("Saturday")
ll.insert("Sunday")

print("Linked list: ", end = "")
ll.print()
print("isCycle(): ", ll.isCycle())

print("Adding a cycle in the linked list...")
# Adding a cycle in the linked list
ll.tail.next = ll.head # Now next of tail points to head of the list
print("isCycle(): ", ll.isCycle())

OUTPUT:

FOR ANY DOUBT DROP A COMMENT