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:

Build the result list and return its head.

Example 1:

**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:

**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

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