Random integer with conditions

Question

I have a PHP script where I have an array of integers, let's say $forbidden.

I want to get a random integer from 1 to 400 that is not in $forbidden.

Of course, I don't want any loop which breaks when rand gives a working result. I'd like something more effective.

How do you do this ?

Answer 1

Place all forbidden numbers in an array, and use array_diff from range(1,400). You'll get an array of allowed numbers, pick a random one with array_rand().

<?php

$forbidden = array(2, 3, 6, 8);
$complete = range(1,10);
$allowed = array_diff($complete, $forbidden);

echo $allowed[array_rand($allowed)];

This way you're removing the excluded numbers from the selection set, and nullifying the need for a loop :)