lc21~lc30

21.

class ListNode:
    def __init__(self,x):
        self.val = x
        self.next = None
    
class Solution:
    def mergeTwoLists(self, l1, l2):
        
        res = pre = ListNode(0)
        
        while l1 and l2:
            if l1.val <= l2.val:
                val = l1.val
                l1 = l1.next
                
            else:
                val = l2.val
                l2 = l2.next
            #print(val)
            pre.next = pre = ListNode(val)
            
        if l1:
            pre.next = l1
            
        if l2:
            pre.next = l2
            
        
        return res.next
    

if __name__ == '__main__':
    L1 = ListNode(1)
    L1.next = L11 = ListNode(2)
    L11.next = L12 = ListNode(4)
    
    L2 = ListNode(1)
    L2.next = L21 = ListNode(3)
    L21.next = L22 = ListNode(4)
    L21.next = L22 = ListNode(5)
    
    
    sol = Solution()
    res = sol.mergeTwoLists(L1, L2)
    
    while res:
        print(res.val)
        res = res.next