note 56146 deleted from function.rand by felipe

Note Submitter: Pierre C. 

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I am sorry to tell you this, mark at mmpro dot de, but the function you mentioned looks awfully and unnecessarily slow to me:

At each iteration, you have to check if the generated number is not already in the list, so you end up with a complexity of O(n²)... at best! (In the worst case, the algorithm might just run forever!!!)

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Here is a better (and safer!) way to generate a random array of different numbers:

  - First generate an array, each element filled with a different value (like: 1,2,3,4,5,...,n)

  - Then shuffle your array. In other words, swap each element in your array with another randomly-chosen element in the array.

Now the algorithm has a complexity of O(n), instead of the original O(n²).

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The generation of the array of values is left at the discretion of the programmer (it is down to his/her needs to determine how the values should be reparted).

The shuffling of the array should go like this (WARNING: CODE NOT TESTED !!!):

$length = count($array) ;

for($i=0; $i<$length; $i++) {

  // Choosing an element at random
  $randpos = rand(0, $length-1) ;

  // Swapping elements
  $temp = $array[$randpos] ;
  $array[$randpos] = $array[$i] ;
  $array[$i] = $temp ;
}

return $array ;