# Leetcode 21. Merge Two Sorted Lists
將兩個已排序之linked list合併。
## 想法
直接使用合併排序法

程式碼:

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def mergeTwoLists(self, l1: ListNode, l2: ListNode) -> ListNode:
        if(not l1 and not l2):
            return None
        i = 0
        while(l1 or l2):
            if(i==0):
                i+=1
                ans = ListNode(0)
                target = ans
            if(not l1):
                ans.next = l2
                l2 = l2.next
            elif(not l2):
                ans.next = l1
                l1 = l1.next
            else:
                if(l2.val>l1.val):
                    ans.next = l1
                    l1 = l1.next
                else:
                    ans.next = l2
                    l2=l2.next
            ans = ans.next
        return target.next