# 1669. Merge In Between Linked Lists

<https://leetcode.com/problems/merge-in-between-linked-lists>

## Description

You are given two linked lists: `list1` and `list2` of sizes `n` and `m` respectively.

Remove `list1`'s nodes from the `ath` node to the `bth` node, and put `list2` in their place.

The blue edges and nodes in the following figure incidate the result:

![](https://assets.leetcode.com/uploads/2020/11/05/fig1.png) *Build the result list and return its head.*

**Example 1:**

![](https://assets.leetcode.com/uploads/2020/11/05/merge_linked_list_ex1.png)

```
**Input:** list1 = [0,1,2,3,4,5], a = 3, b = 4, list2 = [1000000,1000001,1000002]
**Output:** [0,1,2,1000000,1000001,1000002,5]
**Explanation:** We remove the nodes 3 and 4 and put the entire list2 in their place. The blue edges and nodes in the above figure indicate the result.
```

**Example 2:**

![](https://assets.leetcode.com/uploads/2020/11/05/merge_linked_list_ex2.png)

```
**Input:** list1 = [0,1,2,3,4,5,6], a = 2, b = 5, list2 = [1000000,1000001,1000002,1000003,1000004]
**Output:** [0,1,1000000,1000001,1000002,1000003,1000004,6]
**Explanation:** The blue edges and nodes in the above figure indicate the result.
```

**Constraints:**

* `3 <= list1.length <= 104`
* `1 <= a <= b < list1.length - 1`
* `1 <= list2.length <= 104`

## ac

```java
```