在PHP中生成一个随机数的数组，该数组不接近X先前的元素

Question

I want to generate in PHP an array of random numbers, but each number should not be the same as any of the X (for example 2 ) numbers bofore it and not even close to any of them by a define range (for example 5).

So for example:

• I need numbers between 1 and 100
• i've set my "range" to 5
• the first two generated number are 20 and 50.
• the third number will be a random number between 1 and 100, excluding all the numbers between 15 and 25, and between 45 and 55.

I can't figure out a function to achieve it. Ideally I want to call something like this:

getRandomNumbers( $min, $max, $previous, $range);

where $previous is the number of previous elements to take in consideration when generating the next one and $range is the "proximity" to those number where I don't want the next number to be.

I hope I explained in a decent way my request. :) Please, add a comment if you have any question about it.

Answer 1

I just came up with this:

function getRandomNumbers($min, $max, $previous, $range) {
    static $generated = array();
    $chunk = array_slice($generated, -$previous);

    // Added this infinite loop check to save you some headache.
    if (((($max - $min + 1) / (($range * 2) + 1)) + 1) <= $previous) {
        die("Values set have the potential of running into an infinite loop. Min: $min, Max: $max, Previous: $previous, Range: $range");
    }

    while(true) {
        $number = rand($min, $max);
        $found = true;
        foreach ($chunk as $value) {
            if (in_array($number, range($value-$range, $value+$range))) {
                $found = false;
            }
        }
        if ($found) {
            $generated[] = $number;
            return $number;
        }
    }
}

Test it using this:

for ($i = 1; $i < 25; $i++) {
    echo getRandomNumbers(1, 100, 5, 5) . "<br />";
}

PHPFiddle Link: http://phpfiddle.org/main/code/51ke-4qzs

Edit: Added a check to prevent a possible infinite loop. For example: if you set the following values:

$min = 1;
$max = 100;
$previous = 5;
$range = 12;
echo getRandomNumbers($min, $max, $previous, $range);

Then let's say, in a really unfortunate situation it would generate 13, 38, 63 and 88. So the 5th number cannot be anything between 1 and 25, 26 and 50, 51 and 75, 76 and 100. So it would result in an infinite loop. I've updated the PHPFiddle link as well.

Answer 2

getRandomNumbers( $previous, $range ) {
  //I'm assuming that previous will be an array of your previous X that you don't want to be close to
  $num = getRandomNumber() //However you are doing this now
  foreach( $previous as $key => $value ) {
    if ( ( $value - $range ) > $num && ( $value + $range ) < $num ) {
      return getRandomNumbers($previous, $range);
    }
  }
  //You need to also replace a value in previous
  return num;
}