21-merge-two-sorted-lists.go

package main

func mergeTwoLists(list1 *ListNode, list2 *ListNode) *ListNode {
	if list1 == nil {
		return list2
	}
	if list2 == nil {
		return list1
	}

	if list1.Val <= list2.Val {
		list1.Next = mergeTwoLists(list1.Next, list2)
		return list1
	}
	list2.Next = mergeTwoLists(list1, list2.Next)
	return list2
}