Construct Maximum Sum Linked List from Two Sorted Lists in Python

Suppose we have two sorted linked lists, we have to make a linked list that consists of largest sum path from start node to end node. The final list may consist of nodes from both input lists.

When we are creating the result list, we may switch to the other input list only for the point of intersection (two node with the same value in the lists). We have to solve it using constant amount of extra space.

So, if the input is like [6,8,35,95,115,125], [5,8,17,37,95,105,125,135], then the output will be [6,8,17,37,95,115,125,135]

To solve this, we will follow these steps −

• result := None

• previous1 := a, current1 := a

• previous2 := b, current2 := b

• while current1 is not same as None or current2 is not same as None, do

  • res1 := 0, res2 := 0

  • while current1 and current2 are not null and data of current1 is not same as data of current2, do

    • if data of current1 < data of current2, then

      • res1 := res1 + data of current1

      • current1 := next of current1

    • otherwise,

      • res2 := res2 + data of current2

      • current2 := next of current2

  • if current1 is null, then

    • while current2 is not null, do

      • res2 := res2 + data of current2

      • current2 := next of current2

  • if current2 is null, then

    • while current1 is not null, do

      • res1 := res1 + data of current1

      • current1 := next of current1

  • if previous1 is same as a and previous2 is same as b, then

    • result := previous1 when (res1 > res2) otherwise previous2

  • otherwise,

    • if res1 > res2, then

      • next of previous2 := next of previous1

    • otherwise,

      • next of previous1 := next of previous2

  • previous1 := current1

  • previous2 := current2

  • if current1 is not null, then

    • current1 := next of current1

  • if current2 is not null, then

    • current2 := next of current2

• display the content of result.

Example

Let us see the following implementation to get better understanding −

class LinkedList(object):
   def __init__(self, data_set = []):
      self.head = None
      if len(data_set) > 0:
         for item in data_set:
            self.insert_node(item)
   class ListNode(object):
      def __init__(self, d):
         self.data = d
         self.next = None
   def insert_node(self, new_data):
      new_node = self.ListNode(new_data)
      new_node.next = self.head
      self.head = new_node
   def find_max_sum_list(self, a, b):
      result = None
      previous1 = a
      current1 = a
      previous2 = b
      current2 = b
      while current1 != None or current2 != None:
         res1 = 0
         res2 = 0
         while current1 != None and current2 != None and current1.data != current2.data:
            if current1.data < current2.data:
               res1 += current1.data
               current1 = current1.next
            else:
               res2 += current2.data
               current2 = current2.next
         if current1 == None:
            while current2 != None:
               res2 += current2.data
               current2 = current2.next
         if current2 == None:
            while current1 != None:
               res1 += current1.data
               current1 = current1.next
         if previous1 == a and previous2 == b:
            result = previous1 if (res1 > res2) else previous2
         else:
            if res1 > res2:
               previous2.next = previous1.next
            else:
               previous1.next = previous2.next
         previous1 = current1
         previous2 = current2
         if current1 != None:
            current1 = current1.next
         if current2 != None:
            current2 = current2.next
      while result != None:
         print(result.data, end = ' ')
         result = result.next
my_list1 = LinkedList([125,115,95,35,8,6])
my_list2 = LinkedList([135,125,105,95,37,17,8,5])
my_list1.find_max_sum_list(my_list1.head, my_list2.head)

Input

[125,115,95,35,8,6], [135,125,105,95,37,17,8,5]

Output

6 8 17 37 95 115 125 135