[Leetcode] 1669. Merge In Between Linked Lists

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

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def mergeInBetween(self, list1: ListNode, a: int, b: int, list2: ListNode) -> ListNode:

        a_pre_node = None
        b_next_node = None

        pre_node = None
        node = list1
        index = 0
        while node != None:
            if index == a:
                a_pre_node = pre_node
            if index == b:
                b_next_node = node.next
                break
            
            pre_node = node
            node = node.next
            index += 1
        
        a_pre_node.next = list2

        pre_node = None
        node = list2
        while node != None:
            pre_node = node
            node = node.next
            
        pre_node.next = b_next_node

        return list1