def Merge(head1, head2):
if head1 == None: return head2
if head2 == None: return head1
psuhead = ListNode(-1)
tail = psuhead
while head1 and head2:
if head1.val < head2.val:
cur = head1
head1 = head1.next
else:
cur = head2
head2 = head2.next
cur.next = tail.next
tail.next = cur
tail = cur
Print(psuhead)
# link the rest nodes
if head1 == None: head1 = head2
tail.next = head1
head1 = psuhead.next
del psuhead
psuhead = None
return head1
