Hash Table Design – How Hash Maps Work Internally

A hash table stores key-value pairs by computing a hash of the key to determine the array index. The core operation is index = hash(key) % array_size, giving O(1) average access. Collisions occur when different keys hash to the same index. I handle them with chaining — each bucket holds a linked list of entries — or open addressing, where I probe for the next empty slot. Chaining is simpler and degrades gracefully; open addressing has better cache performance but is trickier to implement correctly, especially with deletion. I maintain a load factor (entries / buckets). When it exceeds 0.75, I double the array size and rehash all existing entries — this amortized cost keeps operations at O(1). A good hash function distributes keys uniformly; for strings, I might use polynomial rolling hash. For my design, I would use an array of buckets with chaining, track the load factor, and resize at 0.75. I would also implement proper equals checking since different objects can have the same hash code.