Python Program to Check if Two Lists are Equal

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This is a Python program to check whether two linked lists are the same.

Problem Description

The program creates two linked lists using data items input from the user and checks whether they are the same.

Problem Solution

1. Create a class Node with instance variables data and next.
2. Create a class LinkedList with instance variables head and last_node.
3. The variable head points to the first element in the linked list while last_node points to the last.
4. Define methods append and display inside the class LinkedList to append data and display the linked list respectively.
5. Define a function is_equal which takes two linked lists as arguments.
6. The function is_equal returns True only if the two linked lists are of the same length and contain the same data items.
7. Create two instances of LinkedList and append data to it.
8. Check whether they are the same.

Program/Source Code

Here is the source code of a Python program to check whether two linked lists are the same. The program output is shown below.

class Node:
    def __init__(self, data):
       self.data = data
       self.next = None
 
 
class LinkedList:
    def __init__(self):
        self.head = None
        self.last_node = None
 
    def append(self, data):
        if self.last_node is None:
            self.head = Node(data)
            self.last_node = self.head
        else:
            self.last_node.next = Node(data)
            self.last_node = self.last_node.next
 
 
def is_equal(llist1, llist2):
    current1 = llist1.head
    current2 = llist2.head
    while (current1 and current2):
        if current1.data != current2.data:
            return False
        current1 = current1.next
        current2 = current2.next
    if current1 is None and current2 is None:
        return True
    else:
        return False
 
 
llist1 = LinkedList()
llist2 = LinkedList()
 
data_list = input('Please enter the elements in the first linked list: ').split()
for data in data_list:
    llist1.append(int(data))
 
data_list = input('Please enter the elements in the second linked list: ').split()
for data in data_list:
    llist2.append(int(data))
 
if is_equal(llist1, llist2):
    print('The two linked lists are the same.')
else:
    print('The two linked list are not the same.', end = '')
Program Explanation

1. Two instances of LinkedList are created.
2. The user is prompted to enter the data items for the two lists.
3. The function is_equal determines whether the two linked lists are the same.
4. This result is then displayed.

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Runtime Test Cases
Case 1:
Please enter the elements in the first linked list: 5 8 10 12
Please enter the elements in the second linked list: 5 8 10 12
The two linked lists are the same.
 
Case 2:
Please enter the elements in the first linked list: 12 3 4 5 0
Please enter the elements in the second linked list: 12 3
The two linked list are not the same.
 
Case 3:
Please enter the elements in the first linked list: 4 1
Please enter the elements in the second linked list: 2 19 4
The two linked list are not the same.

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Manish Bhojasia - Founder & CTO at Sanfoundry
Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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