Hash Collision

First learned this at Mari, but I still don’t understand. Update: slowly understanding more now.

A hash collision occurs when different input elements map to the same bucket.

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Collisions are actually more common than you intuitively think. See the Birthday Paradox 99% chance even around 70 people

Unless you want to make a gazillion buckets, we need to make a hash function to reduce the Hash Collisions.


  • Closed Hashing: Use some strategy to find another bucket in the table
  • Open Hashing: Each bucket is actually a pointer to short linked list of records