leetcode hot 100

sylviiiiiia2026-09-07 13:28

234.回文链表

主要是单链表不能倒着读，所以放数组里，然后双指针

python 复制代码

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def isPalindrome(self, head: Optional[ListNode]) -> bool:
        num=[]
        p=head
        while p!=None:
            num.append(p.val)
            p=p.next
        flag=False
        if head!=None:
            flag=True
        i=0
        while i<len(num)//2:
            if num[i]!=num[len(num)-1-i]:
                flag=False
            i+=1
        return flag

141. 环形链表

秒了。

python 复制代码

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution:
    def hasCycle(self, head: Optional[ListNode]) -> bool:
        hashtable=dict()
        p=head
        flag=False
        while p!=None:
            if p in hashtable:
                flag=True
                break
            hashtable[p]=1
            p=p.next
        return flag

142.环形链表2

继续哈希，秒了

python 复制代码

class Solution:
    def detectCycle(self, head: Optional[ListNode]) -> Optional[ListNode]:
        hashtable=dict()
        p=head
        cnt=0
        while p!=None:
            if p in hashtable:
                return p
            hashtable[p]=cnt
            p=p.next
            cnt+=1
        return None