Random Number Question

[jc1328]

Hello,

I'm using the random generator with 20 numbers. rand() %20+1. Is there a way that the random number can only show up once, so I can go through all 20 numbers before it displays the same number twice?

[Banfa]

No. The way to do that is with a shuffle algorithm. You start with an array of the numbers 1 - 20 then you choose 2 numbers and swap them. You do this lots of times and you end up with an array of the numbers 1 - 20 in a random order but with every number appearing once and only once.

[jkmyoung]

Another possible way is to generate 20 random double numbers from 0 - 1, and then use their ordering as 1-20.
eg.
0.242, 0.425, 0.139, 0.932, 0.495
ordered is:
0.138, 0.242, 0.425, 0.495, 0.932
giving you:
3, 1, 2, 5, 4