Perfect Hash Functions

A hash function that generates unique addresses for each possible search key is termed a “perfect hash function”.
Life isn’t always so nice…
The previous hash function example for phone numbers would map both of the phone numbers 475-3456 and 645-3456 to the same address of array[3456].
Thus the example given is NOT a perfect hash function because it generates “collisions”.

A hash function that generates unique addresses for each possible search key is termed a “perfect hash function”.