Merge Two Sorted Lists in Python

Suppose we have two sorted lists A and B. We have to merge them and form only one sorted list C. The size of lists may different.

For an example, suppose A = [1,2,4,7] and B = [1,3,4,5,6,8], then merged list C will be [1,1,2,3,4,4,5,6,7,8]

We will solve this using recursion. So the function will work like below −

• Suppose the lists A and B of function merge()
• if A is empty, then return B, if B is empty, then return A
• if value in A <= value in B, then A.next = merge(A.next, B) and return A
• otherwise, then B.next = merge(A, B.next) and return B

Let us see the implementation to get a better understanding

Example (Python)

 Live Demo

class ListNode:    def __init__(self, data, next = None):       self.val = data       self.next = next    def make_list(elements):       head = ListNode(elements[0])       for element in elements[1:]:          ptr = head          while ptr.next:             ptr = ptr.next          ptr.next = ListNode(element)       return head def print_list(head):    ptr = head    print('[', end = "")    while ptr:       print(ptr.val, end = ", ")       ptr = ptr.next    print(']') class Solution:    def mergeTwoLists(self, l1, l2):       """       :type l1: ListNode       :type l2: ListNode       :rtype: ListNode       """       if not l1:          return l2       if not l2:          return l1       if(l1.val<=l2.val):          l1.next = self.mergeTwoLists(l1.next,l2)          return l1       else:          l2.next = self.mergeTwoLists(l1,l2.next)          return l2 head1 = make_list([1,2,4,7]) head2 = make_list([1,3,4,5,6,8]) ob1 = Solution() head3 = ob1.mergeTwoLists(head1,head2) print_list(head3)

Input

head1 = make_list([1,2,4,7]) head2 = make_list([1,3,4,5,6,8])

Output

[1, 1, 2, 3, 4, 4, 5, 6, 7, 8, ]