HashMap Collision Resolution
Separate Chaining
Use data structure (such as linked list) to store multiple items that hash to the same slot
1. use linked list
Collision: insert item into linked list
Find: compute hash value, then do Find on linked list
2. use BST
O(log N) time instead of O(N). But lists are usually small - not worth the overhead of BSTs
Open addressing (or probing or Closed Hashing)
Search for other slots using a second function and store items in first empty slot that is found
Separate chaining can take up a lot of space...
Given an item X, try cells h0(X), h1(X), h2(X), .., hi(X)
hi(X) = (Hash(X) + F(i)) mod TableSize
(Define F(0) = 0)
Linear: F(i) = i
Quadratic: F(i) = i2
Double Hashing: F(i) = i * Hash2(X)
