PHP: permutations formula but for distinct values

Question

I have been trying to get the results from a simple formula and unable to accomplish the correct results:

For example: Array A,B,C

can return 6 results: Answer: a, b | a, c | b, a | b, c | c, a | c, b

But:

b, a has been used: a, b

c, b has been used: b, c

c, a has been used: a, c

Really only leaving 3 distinct answers.

The method i have been using is:

function permutations($pool, $r = null) {
    $n = count($pool);

    if ($r == null) {
        $r = $n;
    }

    if ($r > $n) {
        return;
    }

    $indices = range(0, $n - 1);
    $cycles = range($n, $n - $r + 1, -1); // count down

    yield array_slice($pool, 0, $r);

    if ($n <= 0) {
        return;
    }

    while (true) {
        $exit_early = false;
        for ($i = $r;$i--;$i >= 0) {
            $cycles[$i]-= 1;
            if ($cycles[$i] == 0) {
                // Push whatever is at index $i to the end, move everything back
                if ($i < count($indices)) {
                    $removed = array_splice($indices, $i, 1);
                    array_push($indices, $removed[0]);
                }
                $cycles[$i] = $n - $i;
            } else {
                $j = $cycles[$i];
                // Swap indices $i & -$j.
                $i_val = $indices[$i];
                $neg_j_val = $indices[count($indices) - $j];
                $indices[$i] = $neg_j_val;
                $indices[count($indices) - $j] = $i_val;
                $result = [];
                $counter = 0;
                foreach ($indices as $indx) {
                    array_push($result, $pool[$indx]);
                    $counter++;
                    if ($counter == $r) break;
                }
                yield $result;
                $exit_early = true;
                break;
            }
        }
        if (!$exit_early) {
            break; // Outer while loop
        }
    }
}

//$result = iterator_to_array(permutations(['a', 'b', 'c', "d", "e", "f", "g", "h", "i", "j", "k" ,"l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z"], 2));
$result = iterator_to_array(permutations(['a', 'b', 'c'], 2));
foreach ($result as $row) {
    print implode(", ", $row) . "<br>";
}
echo count($result);

Ashish Tiwari · Accepted Answer · 2018-03-22 11:05:49Z

3

I have implement my own logic. Hope it will help you out:

<?php
$string = 'a,b,c';
$a = explode(',',$string);

foreach($a as $k => $v){
        $count = count($a);
        for($i = 0; $i < $count; $i ++){
                if($v != $a[$i]){
                        $allCases[] = $v.$a[$i];
                }
        }
}

echo "Total cases found : ".implode(',',$allCases)."\n";

foreach($allCases as $k1 => $v1){
    $allCases[$k1] = sortWord($v1);
}

$allCases = array_unique($allCases);

echo "Distinct case : ".implode(',',$allCases)."\n";

function sortWord($string){
        $stringParts = str_split($string);
        sort($stringParts);
        return implode('', $stringParts);
}

answered Mar 22, 2018 at 11:05

Ashish Tiwari

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