Hashing Problems

Practise 30 hashing problems from basics to advanced in Python, C++, Java, JavaScript and TypeScript.

This track covers frequency counting, lookups, grouping, prefix sums with hash maps, and designing keys for a hash map or set. The problems run from easy to hard, so each idea builds on the one before. Every problem is judged against hidden test cases in five languages.

What you will practise:

• Basics: 10 easy problems such as Common Guests, Neighbourly Subsequence and Majority or Nothing.
• Core Problems: 14 medium problems such as No-Repeat Stretch, Repaint to Repeat and Next Clock Time.
• Hard Problems: 6 hard problems such as Smallest Absent Positive, Formula Atom Counter and Imbalance Total.

Start with the basics, move on to the core problems, and try the hard ones when the pattern feels natural. Every problem comes with worked examples and clear constraints. For a full path across all of DSA, see Revquix 80, Revquix 150 and Revquix 300.