2025-08-21

Leetcode Map of Contents

Takeaways

Check if the number of elements has a bound. For example if you are operating on alphabets you know that there are only 26 alphabets. You don’t have to hash them. You can directly map them to an array.
Hashing is used wherever you want a $O(1)$ find() operation. This trades in memory for runtime
Look for memoizing opportunities. If you are able to store the result in a hash-table, then you can reuse them for other element. Many problems have subproblems that can be used. Especially in $O(n)$ cases where we cannot sort.