Generate Distinct Combinations PHP [closed]

Question

I need an efficient algorithm to generate distinct combinations(not allowed to repeat). Each combination has 5 distint numbers(different numbers) that ranges between 1 and 99. The result must be stored in an array. If possible I would like the numbers and range allowed to be customized. The order of number doesn't matter(01 02 03 = 03 01 02)

 Ex.: 
 01 02 03 04 05
 02 03 04 05 06
 ...

Does anyone could help me to build it? I would like to pick up some random combinations from the array. Nowdays I am generating random combinations using mt_rand but It takes too much time, SO SLOW! I believe happens to repeat so often then takes time to generate new one and new one...

Answer 1

I threw this together quickly, seems to work.

<?php

$range_low = 1;
$range_hi  = 99;
$num_sets  = 10;

$set = generateSet($range_low, $range_hi, $num_sets);

print_set($set);

function generateSet($range_low, $range_hi, $numSets = 5, $numPerSet = 5)
{
    $return  = array();
    $numbers = array();

    for($i = $range_low; $i <= $range_hi; ++$i) {
        $numbers[] = $i;
    }

    for ($s = 0; $s < $numSets; ++$s) {
        $set = array_values($numbers);
        shuffle($set);

        $return[$s] = array();

        for ($i = 0; $i < $numPerSet; ++$i) {
            $val = array_shift($set);
            $return[$s][] = $val; 
        }
    }

    return $return;
}

function print_set($set)
{
    foreach($set as $subset) {
        foreach($subset as $value) {
            echo str_pad($value, 2, '0', STR_PAD_LEFT) . ' ';
        }
        echo "\n";
    }
}

Sample output:

90 75 89 43 57 
24 54 38 35 10 
77 21 55 33 83 
37 15 61 09 44 
25 31 85 17 20 
48 37 45 13 20 
82 70 74 64 72 
07 24 33 64 45 
34 13 39 33 05 
13 77 87 70 64 

To Fisher-Yates shuffle the array, see this comment on shuffle for a function you could use in place of shuffle.

Hope that helps.

Answer 2

If you really absolutely need a full set of every possible combination:

function combinations($set,$length) { 
  $combinations = array(); 

  $setCount = count($set);  
  for($i = 0, $n = $setCount; $i <= ($n - $length); $i++) { 
    $combination = array(); 
    $combination[] = $set[$i]; 

    if($length > 1) { 
      $combination = array_merge( 
        $combination, 
        combinations(array_slice($set,1+$i), $length-1) 
      ); 
    } 

    $combinations[] = $combination; 
  } 

  return $combinations; 
} 

$allYourNumbers = range(1,99);
$allCombinations = combinations($allYourNumbers, 5);

Then you can shuffle $allCombinations and extract as many as you want, but you'll need a lot of memory and a lot of time... doing this can never be efficient

Answer 3

Here's the simple code that should run rather fast and do what you describe.

$numbers = range(1, 99); // numbers to pick from
$length = 5; // amount of items in the set
$sets_amount = 15; // amount of sets you want to generate
shuffle($numbers); // randomize

function get_set($length, &$numbers) {
    return array_splice($numbers, 0, $length);
}

for ($i = 0; $i < $sets_amount; $i++)
    print_r(get_set($length, $numbers));

Note: it only works when you need a few combinations. You don't state that you want all of the possible ones, so I thought if you need just a bunch of them - here's very quick and easy way to do it.

For a bit slower (the more you generate - the slower it goes), but that generates any amount of sets, you can use this code.

$numbers = range(1, 99); // numbers to pick from
$length = 5; // amount of items in the set
$sets_amount = 200; // amount of sets you want to generate
$existing = array(); // where we store existing sets
$shuffle_period = count($numbers) - $length - 1; // how often we re-randomize the elements
$j = 0;

for ($i = 0; $i < $sets_amount; $i++, $j++) {
    if (!($i % $shuffle_period)) {
        shuffle($numbers); // randomize at first go and on $shuffle_period
        $j = 0;
    }
    do {
        $arr = array_slice($numbers, $j, $length);
    } while (in_array($arr, $existing));
    $existing[] = $arr;
}

print_r($existing);