def addTwoNumbers(self, l1, l2):
"""
:type l1: ListNode
:type l2: ListNode
:rtype: ListNode
"""
dummy = ListNode(0)
ptr, s = dummy, 0
while l1 or l2 or s >= 10:
s //= 10
if l1:
s += l1.val
l1 = l1.next
if l2:
s += l2.val
l2 = l2.next
ptr.next = ListNode(s % 10)
ptr = ptr.next
return dummy.next
def addTwoNumbers_pre(self, l1, l2):
"""
:type l1: ListNode
:type l2: ListNode
:rtype: ListNode
"""
dummy = ListNode(0)
current, carry = dummy, 0
while l1 or l2 or carry:
val = carry
if l1:
val += l1.val
l1 = l1.next
if l2:
val += l2.val
l2 = l2.next
carry = val // 10
current.next = ListNode(val % 10)
current = current.next
return dummy.next
def mergeTwoLists(self, l1, l2):
"""
:type l1: ListNode
:type l2: ListNode
:rtype: ListNode
"""
dummy = p = ListNode(0)
while l1 and l2:
if l1.val < l2.val:
p.next = l1
l1 = l1.next
else:
p.next = l2
l2 = l2.next
p = p.next
p.next = l1 or l2
return dummy.next