On 1/31/07, [EMAIL PROTECTED] <[EMAIL PROTECTED]> wrote:
>
> ok, this is a lame attempt - can someone explain if it's correct, or
> why not :
>
> int limited_rand() {
> return rand() % 8 + 1;
> }
>
> value = limited_rand() % 3 + limited_rand();
There's no meaning to do mod 8 in your limited_rand() because rand returns
number between 1 and 5.
And your code never returns 1.
Here's my lame attempt. Output is uniformly distributed if input is so.
1 -> 20.065%
2 -> 19.986%
3 -> 19.989%
4 -> 19.964%
5 -> 19.996%
1 -> 14.352%
2 -> 14.302%
3 -> 14.281%
4 -> 14.285%
5 -> 14.295%
6 -> 14.252%
7 -> 14.233%
/* */
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
int rand5()
{
return (rand() % 5)+1;
}
int rand2()
{
int bit;
while((bit=rand5())==5);
return bit%2;
}
int rand7()
{
int sum;
while( (sum = rand2() + rand2()*2 + rand2()*4) == 0);
return sum;
}
int main()
{
int freq1[6];
int freq2[8];
memset(freq1, 0, sizeof(freq1));
memset(freq2, 0, sizeof(freq2));
const int ITER = 1000000;
for(int i=0; i<ITER; i++) {
freq1[rand5()]++;
freq2[rand7()]++;
}
for(int i=1; i<=5; i++)
printf("%d -> %.3lf%%\n", i, double(freq1[i])/ITER*100);
printf("\n\n");
for(int i=1; i<=7; i++)
printf("%d -> %.3lf%%\n", i, double(freq2[i])/ITER*100);
return 0;
}
But of course it is not guaranteed to terminate but it works usually :-)
atamurat
>
>
> On Jan 31, 7:29 am, "Ming \(Amos\) Zhang" <[EMAIL PROTECTED]> wrote:
> > It's not uniformly distributed, suppose the given random generator is
> > uniformly distributed
> >
> > -----Original Message-----
> > From: algogeeks@googlegroups.com [mailto:[EMAIL PROTECTED] On
> >
> > Behalf Of Sandesh
> > Sent: Tuesday, January 30, 2007 11:09 PM
> > To: Algorithm Geeks
> > Subject: [algogeeks] Re: (need help) How to solve this random number
> > generatioin problem?
> >
> > suppose "given" function returns the random numbers between 1 -5 then
> > you can have
> >
> > (given + given) % 7 +1
> >
> > which will generate between 1 and 7 .
> >
> > -Sandesh Hegde
> >
> > On Jan 31, 6:57 am, "Jialin" <[EMAIL PROTECTED]> wrote:
> > > Question:
> >
> > > Given a program which can generate one of {1, 2, 3, 4, 5} randomly.
> > > How can we get another generator which can generate one of
> > > {1,2,3,4,5,6,7} randomly?
> >
> > > Thank you!
>
>
> >
>
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