Count pairs from two linked lists whose sum is equal to a given value


  • Difficulty Level : Easy
  • Last Updated : 07 Jan, 2021

Given two linked lists(can be sorted or unsorted) of size n1 and n2 of distinct elements. Given a value x. The problem is to count all pairs from both lists whose sum is equal to the given value x.
Note: The pair has an element from each linked list.
Examples: 
 

Input : list1 = 3->1->5->7
        list2 = 8->2->5->3
        x = 10
Output : 2
The pairs are:
(5, 5) and (7, 3)

Input : list1 = 4->3->5->7->11->2->1
        list2 = 2->3->4->5->6->8-12
        x = 9         
Output : 5


# Python3 implementation to count pairs from both linked
# lists whose sum is equal to a given value

# A Linked list node
class Node:
	def __init__(self,data):
		self.data = data
		self.next = None

# function to insert a node at the
# beginning of the linked list

def push(head_ref,new_data):
	new_node=Node(new_data)
	#new_node.data = new_data
	new_node.next = head_ref
	head_ref = new_node
	return head_ref


# function to count all pairs from both the linked lists
# whose sum is equal to a given value
def countPairs(head1, head2, x):
	count = 0
	
	#struct Node p1, p2
	
	# traverse the 1st linked list
	p1 = head1
	while(p1 != None):

		# for each node of 1st list
		# traverse the 2nd list
		p2 = head2
		while(p2 != None):

			# if sum of pair is equal to 'x'
			# increment count
			if ((p1.data + p2.data) == x):
				count+=1
			p2 = p2.next
			
		p1 = p1.next
	# required count of pairs	
	return count


# Driver program to test above
if __name__=='__main__':

	head1 = None
	head2 = None
	
	# create linked list1 3.1.5.7
	head1=push(head1, 7)
	head1=push(head1, 5)
	head1=push(head1, 1)
	head1=push(head1, 3)
	
	# create linked list2 8.2.5.3
	head2=push(head2, 3)
	head2=push(head2, 5)
	head2=push(head2, 2)
	head2=push(head2, 8)
	
	x = 10
	
	print("Count = ",countPairs(head1, head2, x))
	
# This code is contributed by


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