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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)
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, ]
Updated on: 28-Apr-2020
1K+ Views
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