Plan#

按照专题刷题，而不是随机刷题。同一个专题，一个套路可以解决多个题目，刷题效率高。此外，这能让你从不同的角度去观察、思考同一个算法，从而深刻地理解算法的本质。螺旋上升式学习：先完成难度分 ≤1700 的题目。把各个题单、各个知识点的基础题刷一遍，再刷更难的题目。难度分低的题目一般只会考察一个知识点，而难度分高的题目会同时考察多个知识点。

https://leetcode.cn/discuss/post/3141566/ru-he-ke-xue-shua-ti-by-endlesscheng-q3yd/

Degree of Completion#

Sliding Window: 2026.1.19 - 2026.1.23#

At most k distinct elements (by using len(cnt) to check if the window is valid)
At most k occurrences of each element (by using cnt[s[r]] > k to check if the window is valid. If adding s[r] makes the window not valid, we need shrink the window to make it valid again)
Exactly K Distinct Elements = At most(K) - At most(K-1)
Some variant questions:
- Including exactly 5 vowels(other character are not vowels) need to divide and conquer firstly. and then do the at most
- exactly