leetcode 141. 环形链表
字典/哈希
class Solution:
def hasCycle(self
, head
: ListNode
) -> bool:
nodemap
= defaultdict
(int)
p
= head
while p
:
nodemap
[p
]+=1
if nodemap
[p
]>1:
return True
p
= p
.next
return False
它还要O(1)内存。能想到的就是依次保存某一个节点，然后判断是否再次访问，但是这样时间不优。
快慢指针
快慢指针判断环，这个的确不知道。
class Solution:
def hasCycle(self
, head
: ListNode
) -> bool:
if not head
or not head
.next:
return False
turtle
= head
rabbit
= head
.next
while True:
if turtle
==rabbit
:
return True
turtle
= turtle
.next
if not rabbit
or not rabbit
.next:
break
rabbit
= rabbit
.next.next
return False
67. 二进制求和
class Solution:
def addBinary(self
, a
: str, b
: str) -> str:
return bin(int(a
,2)+int(b
,2)).replace
('0b','')
299. 猜数字游戏
class Solution:
def getHint(self
, secret
: str, guess
: str) -> str:
count_secret
= [0]*10
count_guess
= [0]*10
bulls
= 0
for i
in range(len(secret
)):
if secret
[i
]==guess
[i
]:
bulls
+=1
else:
count_guess
[ord(guess
[i
])-48]+=1
count_secret
[ord(secret
[i
])-48]+=1
return str(bulls
)+"A"+str(sum(map(lambda x
,y
:min(x
,y
),count_guess
,count_secret
)))+"B"
