Given two polynomial numbers represented by a linked list. The task is to complete the function addPolynomial() that adds these lists meaning adds the coefficients who have the same variable powers.
Note:  Given polynomials are sorted in decreasing order of power.

Example 1:

Input:
LinkedList1:  (1,x2) 
LinkedList2:  (1,x3)
Output:
1x^3 + 1x^2
Explanation: Since, x2 and x3 both have
different powers as 2 and 3. So, their
coefficient can't be added up.

Example 2:

Input:
LinkedList1:  (1,x3) -> (1,x2)
LinkedList2:  (3,x3) -> (4,x2)
Output:
4x^3 + 6x^2
Explanation: Since, x3 has two different
coefficients as 3 and 1. Adding them up
will lead to 4x3. Also, x2 has two
coefficients as 4 and 2. So, adding them
up will give 6x2.

Your Task:
The task is to complete the function addPolynomial() which should add the polynomial with same powers return the required polynomial in decreasing order of the power in the form of a linked list.
Note: Try to solve the question without using any extra space.

Expected Time Complexity: O(N+M)
Expected Auxiliary Space: O(1)

Constraints:
1 <= N, M <= 10⁵
1 <= x, y <= 10⁶