A polynomial linked list is a special type of linked list where every node represents a term in a polynomial expression. Each node has three attributes: coefficient: an integer representing the number multiplier of the term. The coefficient of the term 9x4 is 9. power: an integer representing the exponent. The power of the term 9x4 is 4. next: a pointer to the next node in the list, or null if it is the last node of the list. For example, the polynomial 5x3 + 4x - 7 is represented by the polynomial linked list illustrated below: The polynomial linked list must be in its standard form: the polynomial must be in strictly descending order by its power value. Also, terms with a coefficient of 0 are omitted. Given two polynomial linked list heads, poly1 and poly2, add the polynomials together and return the head of the sum of the polynomials. PolyNode format: The input/output format is as a list of n nodes, where each node is represented as its [coefficient, power]. For example, the polynomial 5x3 + 4x - 7 would be represented as: [[5,3],[4,1],[-7,0]]. Example 1: Input: poly1 = [[1,1]], poly2 = [[1,0]] Output: [[1,1],[1,0]] Explanation: poly1 = x. poly2 = 1. The sum is x + 1. Example 2: Input: poly1 = [[2,2],[4,1],[3,0]], poly2 = [[3,2],[-4,1],[-1,0]] Output: [[5,2],[2,0]] Explanation: poly1 = 2x2 + 4x + 3. poly2 = 3x2 - 4x - 1. The sum is 5x2 + 2. Notice that we omit the "0x" term. Example 3: Input: poly1 = [[1,2]], poly2 = [[-1,2]] Output: [] Explanation: The sum is 0. We return an empty list. Constraints: 0 <= n <= 104 -109 <= PolyNode.coefficient <= 109 PolyNode.coefficient != 0 0 <= PolyNode.power <= 109 PolyNode.power > PolyNode.next.power