Friday, June 8, 2007

hash search, briefly

hash function produces a table *address* for each input key -- no comparison required. Therefor hash represents the 2nd major type of search algorithm, after comparison-based algorithms like Binary Search Tree, or red-black tree

usually the fastest choice for symbol table search

widely used.

constant time for insert and search, but not some other operations like ... sort.

hash output should be evenly distributed across table addresses.

modular hashing should use large prime numbers but why? P174 [[java generics]]

modular hashing need adjustment for long alphanumeric keys cos hardware can't handle 4049040490934 bits for a single variable. Perhaps apply mod-multiple(by 256)-add to (MSB, next MSB, next next MSB..)

Step 1 of hashing algorithm: hashcode(key) to convert key into table address
Step 2 of hashing algorithm: collision resolution -- separate chaining. One separate unordered linked list per shared table-address

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