today we are going to learn how to merge a linked list into another linked list. like we have two linked lists as you see in the images given below.

The first linked list has four nodes.

Merge two linked list Data structures and algorithms

a second linked list has three nodes.

Merge two linked list Data structures and algorithms

so we want to merge the second list into the first list. so first we need to find the reference of the last node of the first linked list.

Merge two linked list Data structures and algorithms

and then we store the second linked list's first node's reference into the linked part of the last of the first linked list. 

Merge two linked list Data structures and algorithms

so now the second linked list is merged into the first linked list.

Python program for merging one list into another linked list.

class Node:

    def __init__(self,value):
        self.info = value
        self.link = None
class SingleLinkedList:

    def __init__(self):
        self.start = None
    def display_list(self):
        if self.start is None:
            print("List is empty")
            return        else:
            print("List is : ")
            p = self.start
            while p is not None:
                print(p.info, " ", end='')
                p = p.link
            print()

    def insert_at_end(self, data):
        temp = Node(data)
        if self.start is None:
            self.start = temp
            return
        p = self.start
        while p.link is not None:
            p = p.link
        p.link = temp

    def create_list(self):
        n = int(input("Enter the numer of nodes : "))
        if n == 0:
            return        for i in range(n):
            data = int(input("Enter the element to be inserted : "))
            self.insert_at_end(data)

    def concatenate(self, list2):
        if self.start is None:
            self.start = list2.start
            return
        if list2.start is None:
            return
        p = self.start
        while p.link is not None:
            p = p.link

        p.link = list2.start

############################################################
list1 = SingleLinkedList()

list2 = SingleLinkedList()

print("Enter first list :- ")
list1.create_list()
print("Enter second list :- ")
list2.create_list()

print("First ")
list1.display_list()
print("Second ")
list2.display_list()

list1.concatenate(list2)
print("First ")
list1.display_list()

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