?
Solved

Hash tables

Posted on 2000-03-27
5
Medium Priority
?
292 Views
Last Modified: 2010-04-02
Hi. I'm trying to implement the following hash functions.
1. h(x)= 1 + (x/k) * M
2. h(x)= 1 + x mod M
3. h(x)=1 + @x mod M

Where M is the table size. They should change keys into integers in the range from 1 to M. I'm using this to generate the numbers and send them to the hash function:

#include<iostream.h>
#include<stdlib.h>
main()
{
 int tablesize=32;
 int a[200];
 for(int i=0;i<200;i++)
 {
      i=rand()%5001;
        h(x)=hash(tablesize,i)
   }
 return 0;
}

1. How do I make the hash function?
2. Can hashing be used with text? Can you provide some examples?
Thanx
0
Comment
Question by:q_low
  • 3
  • 2
5 Comments
 
LVL 10

Expert Comment

by:RONSLOW
ID: 2662927
something like this would probably do...

int hash1(int M, int x) { return 1 + (x / k) * M; }
int hash2(int M, int x) { return 1 + x % m; }
int hash3(int M, int x) { return 1 + ???x % m; }
// whatever @x means
// don't know what you're talking about there
// you'll have to code that yourself

static int method = 1;

int hash(int M, int x) {
  switch (method) {
  case 1: return hash1(M,x);
  case 2: return hash1(M,x);
  case 3: return hash1(M,x);
  }
  return 0; // not a valid hash method
}

You can then set method to be 1, 2 or 3 as required.

And I think you want you code to say
  int x;
  for(int i=0;i<200;i++) {
    x=rand()%5001;
    a[x]=hash(tablesize,x);
  }
And then print out (or do something with) the hash values rather than just end the program.

To use with text, you usually loop for each each character, hash it and combine with the overall running hash value (eg add, or shift and add or whatever).  There are lots of examples around of hashing.

0
 

Author Comment

by:q_low
ID: 2663948
in the first equation k will be the key.
what does the key means if i have a table of size 32?
0
 

Author Comment

by:q_low
ID: 2667660
....
0
 
LVL 10

Accepted Solution

by:
RONSLOW earned 150 total points
ID: 2672700
the way you have shown the code, x is the key.  k being the key doesn't make sense .. because then what is x and where does k come from.

if your table size is 32, then .. well, your table size is 32.  Don't think it means anything in particular.

I think I answred you question satisfactorily.

0
 

Author Comment

by:q_low
ID: 2692064
thanx
0

Featured Post

Free Tool: Site Down Detector

Helpful to verify reports of your own downtime, or to double check a downed website you are trying to access.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

Question has a verified solution.

Are you are experiencing a similar issue? Get a personalized answer when you ask a related question.

Have a better answer? Share it in a comment.

Join & Write a Comment

Written by John Humphreys C++ Threading and the POSIX Library This article will cover the basic information that you need to know in order to make use of the POSIX threading library available for C and C++ on UNIX and most Linux systems.   [s…
This article will show you some of the more useful Standard Template Library (STL) algorithms through the use of working examples.  You will learn about how these algorithms fit into the STL architecture, how they work with STL containers, and why t…
The viewer will learn how to pass data into a function in C++. This is one step further in using functions. Instead of only printing text onto the console, the function will be able to perform calculations with argumentents given by the user.
The viewer will be introduced to the member functions push_back and pop_back of the vector class. The video will teach the difference between the two as well as how to use each one along with its functionality.

569 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question