128. 最长连续序列 (Python3)

Problem: 128. 最长连续序列

思路

参考：

• https://leetcode.cn/problems/longest-consecutive-sequence/solutions/276931/zui-chang-lian-xu-xu-lie-by-leetcode-solution/?envType=study-plan-v2&envId=top-100-liked

• https://leetcode.cn/problems/longest-consecutive-sequence/solutions/2362995/javapython3cha-xi-biao-ding-wei-mei-ge-l-xk4c/?envType=study-plan-v2&envId=top-100-liked

解题方法

1. 使用set()构建 hash table，并非总是依赖 dict，应该根据实际选取；

2. set 天然的适合去重，这道题认识到去重是很重要的；

3. 如何判断一个子序列首部？num-1 不在 set 里！

4. 如何判断一个子序列尾部？num+1 不在 set 里！

额外讨论（来自 GPT）

1 python中使用set()构建hash table

In Python, a set is implemented using a hash table. This is why sets have very efficient performance characteristics for certain operations, especially for checking membership, adding elements, and removing elements. Here’s a brief overview of how this works:

1. Hash Table Mechanism:

• A hash table is a data structure that uses a hash function to map values (keys) to positions in an array.

• In the case of a Python set, the elements of the set are the keys in the underlying hash table.

2. Efficient Operations:

• Membership Testi