How does a hash map (hash table) work internally?

A hash map stores key-value pairs using a hash function to map keys to bucket indices. **Core ideas:** - Compute `hash(key)` then `index = hash % capacity`. - Store entries in a bucket. **Collisions:** multiple keys can map to the same bucket. - **Chaining:** bucket holds a list/tree of entries. - **Open addressing:** probe for the next free slot (linear/quadratic probing). **Resizing:** When load factor is high, rehash into a bigger table. **Complexity:** Average O(1) for get/put; worst-case can degrade to O(n) if collisions are extreme or hash is poor.