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# 1634. Add Two Polynomials Represented as Linked Lists

<https://leetcode.com/problems/add-two-polynomials-represented-as-linked-lists>

## Description

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 `**9**x4` is `9`.
* `power`: an integer representing the exponent. The power of the term `9x**4**` 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:

![](https://assets.leetcode.com/uploads/2020/09/30/polynomial2.png)

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:**

![](https://assets.leetcode.com/uploads/2020/10/14/ex1.png)

```

**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`

## ac

```java
```