Posted by Chung Leong on 07/17/06 23:22

Rik wrote:
> Hmmz, you've got a point.
> If the second case:
> function get_rand_except($start,$end,$not){
> if(!is_array($not) || empty($not)) return mt_rand($start,$end); //we
> don't bother when $not is empty....
> $values = range($start,$end); //numbers in range
> $choosable = array_diff($values,$not); //remove unwanted numbers
> if(count($choosable)==0) return false; //check wether we can choose
> anything
> $choosable = array_value($choosable): //to reset array keys
> return $choosable[mt_rand(0,count($choosable)-1]; //return by random key
> }
>
> Grtz,
> --
> Rik Wasmus

That's rather expensive. There is really no need to remap every number
within the range. You only need to remap the holes. Say you want a
random number from 1 to 100, excluding 34, 62, and 87. What we can do
is map 34 to 100, 62 to 99, 87 to 98 with a hash table. Then we get a
random number from 1 to 97 and check the hash for a replacement value.

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