<?php
  // Based on code from:
  // http://stackoverflow.com/questions/14389180/algorithm-for-probability-when-looping-over-a-randomly-ordered-array
  // http://math.stackexchange.com/questions/280792/determining-probability-in-a-random-loop/280948#280948
  // -------------

  // Taken from php.net/shuffle user notes
  function shuffle_assoc($array) {
    $keys = array_keys($array);
    shuffle($keys);
    foreach($keys as $key) {
      $new[$key] = $array[$key];
    }
    return $new;
  }

  $i = 1000000; // How many tests to perform

  // This is my rule list.  Each key is a simple color
  // and each value is a probability represented as a percent
  $rules = array(
    'black' => 20,
    'white' => 10,
    'red' => 40,
    'green' => 5,
    'blue' => 25,
  );

  // Initialize the scores array with all 0's
  // The "outs" will be used when the probability does not
  // occur in any of the rules
  $scores = array('outs' => 0);
  foreach($rules as $k => $v) { 
    $scores[$k] = 0;
  }

  $count = count($rules);

  for($x = 0; $x < $i; $x++) { 
    $rules = shuffle_assoc($rules);

    $accumulated_probability = 0;
    $rand = mt_rand(1,100);
    foreach($rules as $k => $probability) {
      $actual_probability = $probability + $accumulated_probability;
      $accumulated_probability = $probability + $accumulated_probability;

      if($rand > $actual_probability) { 
        continue; 
      } else {
        $scores[$k]++;
        continue 2;
      }
    }
    $scores['outs']++;
  }


  foreach($scores as $k => $v) { 
    echo "$k: " . (($v/$i)*100) . "% ($v/$i)\n";
  }

?>