# Solving Leetcode Interviews in Seconds with AI: Merge In Between Linked Lists


	# Introduction
	In this blog post, we will explore how to solve the LeetCode problem "1669" using AI. LeetCode is a popular platform for preparing for coding interviews, and with the help of AI tools like [Chatmagic](https://www.chatmagic.app), we can generate solutions quickly and efficiently - helping you pass the interviews and get the job offer without having to study for months.

	# Problem Statement
	> 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 indicate the result:  Build the result list and return its head.   Example 1:   Input: list1 = [10,1,13,6,9,5], a = 3, b = 4, list2 = [1000000,1000001,1000002] Output: [10,1,13,1000000,1000001,1000002,5] 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  

	# Explanation
	Here's the breakdown of the solution:

*   **Locate Insertion Points:** Traverse `list1` to find the nodes at positions `a-1` and `b+1`. These will be the points where `list2` needs to be inserted.
*   **Link Lists:**  Connect the node at `a-1` in `list1` to the head of `list2`. Then, traverse `list2` to find its tail. Connect the tail of `list2` to the node at `b+1` in `list1`.
*   **Handle Edge Cases:** Ensure the solution works correctly if `a` is 0 (insert at the beginning) or if `b` is the last element of list1

*   **Time Complexity:** O(n + m), where n is the length of list1 and m is the length of list2.  **Space Complexity:** O(1) - constant extra space.

	
	# Code
	```python
	class ListNode:
    def __init__(self, val=0, next=None):
        self.val = val
        self.next = next

def mergeInBetween(list1: ListNode, a: int, b: int, list2: ListNode) -> ListNode:
    """
    Merges list2 into list1 between the ath and bth nodes of list1.
    """
    # Find the node before the insertion point (a-1)
    pre_a = list1
    for _ in range(a - 1):
        pre_a = pre_a.next

    # Find the node after the deletion point (b+1)
    post_b = list1
    for _ in range(b + 1):
        post_b = post_b.next

    # Connect list1 before 'a' to the head of list2
    pre_a.next = list2

    # Find the tail of list2
    tail_list2 = list2
    while tail_list2.next:
        tail_list2 = tail_list2.next

    # Connect the tail of list2 to list1 after 'b'
    tail_list2.next = post_b

    return list1
	```