#315 · #1669 · Merge In Between Linked Lists(合并两个链表)

You are given two linked lists list1 and list2, and two integers a and b. Remove the nodes of list1 from index a to index b inclusive, and insert list2 in their place. Return the head of the resulting list. Constraints: 3 <= list1.length <= 10^4, 1 <= list2.length <= 10^4, 0 <= a <= b < list1.length - 1.