On Sep 7, 11:56 am, ankur aggarwal <ankur.mast....@gmail.com> wrote: > Given a random number generator that generates numbers in the range 1 to > 5, how can u create a random number generator to generate numbers in the > range 1 to 7. (remember that the generated random numbers should follow a > uniform distribution in the corresponding range)
If you generate 2 random numbers, there are 25 possible outcomes. This doesn't map nicely to the 7 desired outcomes. The standard way out of this mess is to ignore 4 outcomes leaving 21. Then map these to the range 1 to 7: int n; do n = (random1to5() - 1) * 5 + (random1to5() - 1); while n >= 7 * 3; return 1 + n % 7 You can avoid throwing away random numbers with higher probabilty by generating more to begin with. For example, generating 3 provides 5 * 5 * 5 = 125 possible outcomes. Discard 6 cases to leave 119 = 17 * 7. So we have int n; do n = (random1to5() - 1) * 5 * 5 + (random1to5() - 1) * 5 + (random1to5() - 1); while n >= 7 * 17; return 1 + n % 7 The probability of discarding a number is 4/25 in the first case, but only 6 / 125 in the second. --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Algorithm Geeks" group. To post to this group, send email to algogeeks@googlegroups.com To unsubscribe from this group, send email to algogeeks+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/algogeeks -~----------~----~----~----~------~----~------~--~---
