Hash tables

A hash table uses a hash function to decide where to store an item. In this exercise, a simple modulus operation maps an ID to one of several buckets.

KEY CONCEPTThe bucket rule

With five buckets, the bucket index is id % 5. For example, both 6 % 5 and 11 % 5 produce bucket 1.

Interactive bucket simulator

INTERACTIVE / LIVE

Build a hash table

Change the bucket count, add your own IDs and watch collisions appear.

Live demo

Buckets

5

Insert an IDInsert IDReset

Bucket index = ID % bucket count. More than one ID in the same bucket is a collision.

What happens during a collision?

A collision occurs when different keys map to the same bucket. Collisions are normal; they must be handled correctly. Common approaches include separate chaining and open addressing.

Complexity

Operation	Average case	Worst case
Lookup	O(1)	O(n)
Insert	O(1)	O(n)
Delete	O(1)	O(n)

IMPORTANTThis is a learning hash function

Real hash tables use hashing and resizing strategies more sophisticated than id % bucketCount. The demonstration is intentionally simple so you can see bucket placement.