What is Hash Map Patterns

hash map (key-value store with $O(1)$ lookup) Map provides $O(1)$ average lookup, insertion, and deletion using key-value pairs. You use it when you need fast access to previously seen elements or when counting frequencies. It trades space for time, reducing $O(n)$ lookups to $O(1)$.

You'll see this in two-sum variants, frequency counting, and duplicate detection. If you can explain these concepts in your own words, you'll solve related problems faster under interview pressure.