Python, straightforward
Find the node before a and after b in the list1, then fix the next pointers to join prea and postb nodes with list2:\n\ndef mergeInBetween(self, list1: ListNode
Find the node before a and after b in the `list1`, then fix the next pointers to join `prea` and `postb` nodes with `list2`:\n```\ndef mergeInBetween(self, list1: ListNode, a: int, b: int, list2: ListNode) -> ListNode:\n\tprea = postb = None\n\tdummy = cur = ListNode(next=list1)\n\tfor i in range(b+1):\n\t\tif i == a: prea = cur\n\t\tcur = cur.next\n\tpostb = cur.next\n\n\tprea.next = list2\n\twhile list2.next:\n\t\tlist2 = list2.next\n\n\tlist2.next = postb\n\treturn dummy.next\n```
['Python', 'Python3']