Hash Table

Symbols are stored in a hash table, indexed by a hash function applied to the key value ( e.g., multiply a symbol by itself and take some bits from the middle of the product). The hash function always produces the same value for a given symbol, but is otherwise ``random''. If there is a collision (two different symbols hash to the same value), it is necessary to rehash ( e.g., try the next place in the table).

Insert:	O(1)	Depends on table fullness
Search:	O(1)	Depends on table fullness

The expected time is short for a table that is under 70% full; time depends on fullness but not on table size.

Advantages:

• Fast

• Works for symbols without a natural sort order

Disdvantages:

• More complex code

• Have to find a good hashing function

• Must dedicate a large table, or rehash the table to expand.