要求:求单链表中的倒数第k个结点
思路:使用快慢指针,快的先走k-1步,需要考虑空链表以及k为0
def last_kth(link, k):
if not link or k <= 0:
return None
move = link
while move and k-1 >= 0:
move = move.next
k -= 1
while move:
move = move.next
link = link.next
if k == 0:
return link.val
return None
要求:反转链表
思路:需要考虑空链表,只有一个结点的链表
def reverse_link(head):
if not head or not head.next:
return head
then = head.next
head.next = None
last = then.next
while then:
then.next = head
head = then
then = last
if then:
last = then.next
return head
要求:合并两个排序的链表
思路:使用递归
def merge_link(head1, head2):
if not head1:
return head2
if not head2:
return head1
if head1.val <= head2.val:
ret = head1
ret.next = merge_link(head1.next, head2)
else:
ret = head2
ret.next = merge_link(head1, head2.next)
return ret
要求:判断一棵二叉树是不是另一个的子结构
思路:使用递归
def sub_tree(tree1, tree2):
if tree1 and tree2:
if tree1.val == tree2.val:
return sub_tree(tree1.left, tree2.left) and sub_tree(tree1.right, tree2.right)
else:
return sub_tree(tree1.left, tree2) or sub_tree(tree1.right, tree2)
if not tree1 and tree2:
return False
return True