Random number generation [duplicate]

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Expand a random range from 1-5 to 1-7

Hi, This question is taken from http://blog.seattleinterviewcoach.com/2009/02/140-google-interview-questions.html

Given a function which produces a random integer in the range 1 to 5, write a function which produces a random integer in the range 1 to 7.

I am not getting a way to generate all random numbers 1 to 7 with almost equal probability by using 1 to 5 random generator.

Coul开发者_开发问答d anyone pls solve it ?

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I assume that the function you're given provides uniformly distributed-numbers and it is a strict requirement that the function you need to write also returns uniformly-distributed numbers.

The following pseudo-code illustrates the standard technique (called rejection sampling):

do {
  rand25 = (rand5() - 1) * 5 + rand5; // 1-25
} while (rand25 > 21);
return (rand25 - 1) / 3 + 1;

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What about func() + func() % 3 ?