The fundamentals of Hash tables?

Question

I\'m quite confused about the basic concepts of a Hash table. If I were to code a hash how would I even begin? What is the difference between a Hash table and just a normal

Answer 1

You wouldn't want to use a hash table for 100 randomly generated numbers.

A good way to think about hash tables is to think about value pairs. Let's use students, and say everyone has a student ID number. In your program you store information on students (names, phone numbers, bills, etc). You want to find all of the information about a student using only basic information (name or student ID, for example).

Let's say you have 10,000 students. If you store them all in an array, then you have to loop through the entire array comparing each entry's student ID with the one you are looking for.

If, instead, you "hash" (see below) their student ID number to a position in the array, then you only have to search student's who's numbers have the same hash. Much less work to find what you wanted.

In this example, let's say student IDs are just 6 digit numbers. Our hash function could be use only the bottom 3 digits of the number as the "hash key". Thus 232145 is hashed to array location 145. So then you only need an array of 999 element (each element being a list of students).

That should be a good start for you. You should, of course, read a text book or wikipedia for this kind of info. But I assume you've already done that and are tired of reading.