Hash Set vs Hash Map

Hash Set: stores unique elements. Use when you only care about presence.

• "Have I seen this number?"
• "Is this string in the dictionary?"

Hash Map: stores key-value pairs.

Use when you need to associate data with keys.

• "How many times does each number appear?"
• "What index did I first see this number at?"

In Python, set is a hash set, dict is a hash map. In C++, unordered_set and unordered_map.