1669. Merge In Between Linked Lists

Problem

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

Problem Summary

You are given two linked lists, list1 and list2, containing n and m elements respectively. Delete the nodes from the ath node to the bth node in list1, and connect list2 at the position of the deleted nodes.

Solution Approach

An easy problem that tests basic linked list operations. Pay attention to the case where a == b.

Code

func mergeInBetween(list1 *ListNode, a int, b int, list2 *ListNode) *ListNode {
	n := list1
	var startRef, endRef *ListNode
	for i := 0; i <= b; i++ {
		if i == a-1 {
			startRef = n
		}
		if i == b {
			endRef = n
		}
		n = n.Next
	}
	startRef.Next = list2
	n = list2
	for n.Next != nil {
		n = n.Next
	}
	n.Next = endRef.Next
	return list1
}