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malms · Feb 14th, 2007, 1:30 AM

hi guys,
when i generate k random numbers in range from 1 to 100, usually i got a few numbers that repeat themselves.
how can i generate the k non-repetitive random number?
i tried to do error checking, whether the new generated random number is the same with the old one, but it's not working

thanks

Jimbo · Feb 14th, 2007, 4:00 AM

Aside from using a method which will incur some overhead, you can't. And if it's random, you should allow for the possibility of having a duplicate. You could keep a list of previous numbers and check for a duplicate if you wanted to. Or, you could keep a pool of valid numbers, shuffle it up, and remove randomly indexed values from the shuffled list.

InfoGeek · Feb 14th, 2007, 7:54 AM

or you can do something like...

(Toggle Plain Text)

  for(i=0;i<100;++i)
     a[i] = i+1;

  for(i=0;i<100;++i)
     swap(a[i], a[rand()%100]);

kruptof · Feb 14th, 2007, 9:52 AM

Quote:

Originally Posted by InfoGeek

or you can do something like...

(Toggle Plain Text)

  for(i=0;i<100;++i)
     a[i] = i+1;

  for(i=0;i<100;++i)
     swap(a[i], a[rand()%100]);

you should aslo give srand a call before calling rand or everytime you start the program you will get the same random numbers as you got last time you ran the program

jim mcnamara · Feb 14th, 2007, 12:17 PM

If you are dealing a deck of cards, infogeek's method is what you want. You can deal a card only once. If you are doing something with "random" selections, then repeats have to be allowed, because that is what random means.

Feb 14th, 2007, 1:30 AM	#1
malms Newbie Join Date: Feb 2007 Posts: 1 Rep Power: 0	non-repetitive random number hi guys, when i generate k random numbers in range from 1 to 100, usually i got a few numbers that repeat themselves. how can i generate the k non-repetitive random number? i tried to do error checking, whether the new generated random number is the same with the old one, but it's not working thanks

Feb 14th, 2007, 4:00 AM	#2
Jimbo Battle Programmer Join Date: Feb 2006 Location: Bellevue, WA, USA Posts: 754 Rep Power: 3	Aside from using a method which will incur some overhead, you can't. And if it's random, you should allow for the possibility of having a duplicate. You could keep a list of previous numbers and check for a duplicate if you wanted to. Or, you could keep a pool of valid numbers, shuffle it up, and remove randomly indexed values from the shuffled list. __________________ <insert disclaimer here> <insert shameless plug for Visual Studio here>

Feb 14th, 2007, 7:54 AM	#3
InfoGeek Professional Programmer Join Date: Jun 2005 Location: India, The great. Posts: 435 Rep Power: 4	or you can do something like... (Toggle Plain Text) for(i=0;i<100;++i) a[i] = i+1; for(i=0;i<100;++i) swap(a[i], a[rand()%100]); for(i=0;i<100;++i) a[i] = i+1; for(i=0;i<100;++i) swap(a[i], a[rand()%100]); __________________ PFO - My daily dose of technology.

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Feb 14th, 2007, 12:17 PM	#5
jim mcnamara Hobbyist Programmer Join Date: Jun 2005 Location: New Mexico Posts: 228 Rep Power: 4	If you are dealing a deck of cards, infogeek's method is what you want. You can deal a card only once. If you are doing something with "random" selections, then repeats have to be allowed, because that is what random means.

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