Python Program to Add Corresponding Positioned Elements of Two Linked Lists

This is a Python program to add the corresponding elements of two linked lists.

Problem Description

The program creates two linked lists using data items input from the user and creates a linked list consisting of the sum of data items of the two lists.

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 add_linked_lists which takes two linked lists as arguments.
6. The function add_linked_lists returns a linked list which has its elements as the sum of the data items of the two lists passed to it. If one list is shorter, then the rest of the elements are appended from the longer list.
7. Create two instances of LinkedList and append data to it.
8. Create the sum linked list and display it.

Program/Source Code

Here is the source code of a Python program to add the corresponding elements of two linked lists. 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 display(self):
        current = self.head
        while current is not None:
            print(current.data, end = ' ')
            current = current.next
 
 
def add_linked_lists(llist1, llist2):
    sum_llist = LinkedList()
    current1 = llist1.head
    current2 = llist2.head
    while (current1 and current2):
        sum = current1.data + current2.data
        sum_llist.append(sum)
        current1 = current1.next
        current2 = current2.next
    if current1 is None:
        while current2:
            sum_llist.append(current2.data)
            current2 = current2.next
    else:
        while current1:
            sum_llist.append(current1.data)
            current1 = current1.next
    return sum_llist
 
 
 
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))
 
sum_llist = add_linked_lists(llist1, llist2)
 
print('The sum linked list: ', end = '')
sum_llist.display()

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 add_linked_lists is called to create the sum linked list.
4. This list is then displayed using the display method.

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Runtime Test Cases

Case 1:
Please enter the elements in the first linked list: 1 9 10 15
Please enter the elements in the second linked list: 2 5 4
The sum linked list: 3 14 14 15 
 
Case 2:
Please enter the elements in the first linked list: 3 4 5
Please enter the elements in the second linked list: 
The sum linked list: 3 4 5 
 
Case 3:
Please enter the elements in the first linked list: 7 10
Please enter the elements in the second linked list: 6 5 4 3 2
The sum linked list: 13 15 4 3 2

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