21. 合并两个有序链表

package main
import "fmt"
type ListNode struct {
      Val int
     Next *ListNode
}
//https://leetcode-cn.com/problems/merge-two-sorted-lists/
func mergeTwoLists(l1 *ListNode, l2 *ListNode) *ListNode {
     dummy := &ListNode{}
     cur := dummy
     for {
         if l1==nil&&l2==nil {
             break
         }
         if l1==nil {
             cur.Next = l2
             break
         }
         if l2==nil {
             cur.Next = l1
             break
         }
         if l1.Val<l2.Val {
             cur.Next = l1
             l1 = l1.Next
             cur = cur.Next
         }else {
             cur.Next = l2
             l2 = l2.Next
             cur = cur.Next
         }
     }
     return dummy.Next
}
func main() {
    a1 := &ListNode{Val:  1}
    b1 := &ListNode{Val:  2}
    c1 := &ListNode{Val:  4}
    a2 := &ListNode{Val:  1}
    b2 := &ListNode{Val:  3}
    c2 := &ListNode{Val:  4}
    a1.Next=b1
    b1.Next = c1
    a2.Next = b2
    b2.Next = c2
    h := mergeTwoLists(a1,a2)
    for h!=nil{
        fmt.Println(h.Val)
        h=h.Next
    }
}