golang力扣leetcode 21.合并两个有序链表

package main
type ListNode struct {
  Val  int
  Next *ListNode
}
func mergeTwoLists1(l1 *ListNode, l2 *ListNode) *ListNode {
  if l1 == nil {
    return l2
  }
  if l2 == nil {
    return l1
  }
  var head *ListNode
  if l1.Val > l2.Val {
    head = l2
    head.Next = mergeTwoLists(l1, l2.Next)
  } else {
    head = l1
    head.Next = mergeTwoLists(l1.Next, l2)
  }
  return head
}
func mergeTwoLists2(l1 *ListNode, l2 *ListNode) *ListNode {
  dummy := &ListNode{}
  head := dummy
  for l1 != nil && l2 != nil {
    if l1.Val < l2.Val {
      head.Next = l1
      l1 = l1.Next
    } else {
      head.Next = l2
      l2 = l2.Next
    }
    head = head.Next
  }
  if l1 != nil {
    head.Next = l1
    l1 = l1.Next
    head = head.Next
  } else if l2 != nil {
    head.Next = l2
    l2 = l2.Next
    head = head.Next
  }
  return dummy.Next
}
func main() {
}