题目:
Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.
Example:
Input: 1->2->4, 1->3->4 Output: 1->1->2->3->4->4
solution from discuss:
这是一个链表问题,有迭代和递归方法:
# iteratively
def mergeTwoLists1(self, l1, l2):
dummy = cur = ListNode(0)#注意是()而不是[]
while l1 and l2:
if l1.val < l2.val:
cur.next = l1
l1 = l1.next
else:
cur.next = l2
l2 = l2.next
cur = cur.next
cur.next = l1 or l2 #.next
return dummy.next
# recursively
def mergeTwoLists2(self, l1, l2):
if not l1 or not l2:
return l1 or l2
if l1.val < l2.val:
l1.next = self.mergeTwoLists(l1.next, l2)
return l1
else:
l2.next = self.mergeTwoLists(l1, l2.next)
return l2
# in-place, iteratively
def mergeTwoLists(self, l1, l2):
if None in (l1, l2):
return l1 or l2
dummy = cur = ListNode(0)
dummy.next = l1
while l1 and l2:
if l1.val < l2.val:
l1 = l1.next
else:
nxt = cur.next
cur.next = l2
tmp = l2.next
l2.next = nxt
l2 = tmp
cur = cur.next
cur.next = l1 or l2
return dummy.next
'''