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Hash tables
Posted on 2000-03-27
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
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
-
3
-
2
5 Comments
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.
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.
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