【php】n個の文字からどれを何回使ってもよいので長さrの文字列を作る（重複順列）
問題
a,b,c,d,e,fの文字を使って作れる6文字の文字列をすべて書き出せ。
（重複順列： 異なるn個のものから重複を許してr個とる順列の数は？）
解答例
/**
* 組み合わせ作成関数
*
* @param $a 使用する文字の配列
* @param $l 作成する文字の長さ
* @return 文字の組み合わせ結果の配列
*/
function pat($a, $l)
{
$x = array('');
for ($i = 0; $i < $l; ++$i) {
$_x = array();
foreach ($a as $ak => $av) {
foreach ($x as $xk => $xv) {
$xv .= $av;
$_x[] = $xv;
}
}
$x = $_x;
}
return $x;
}
$a = array('a','b','c','d','e','f');
$l = 6;
var_export(pat($a, $l));
$aが空の配列だったり、$lが長さ0だったりしたときはどうするのがいいでしょうね。
実行結果
array ( 0 => 'aaaaaa', 1 => 'baaaaa', 2 => 'caaaaa', 3 => 'daaaaa', 4 => 'eaaaaa', 5 => 'faaaaa', 6 => 'abaaaa', 7 => 'bbaaaa', 8 => 'cbaaaa', 9 => 'dbaaaa', 10 => 'ebaaaa', 11 => 'fbaaaa', 12 => 'acaaaa', 13 => 'bcaaaa', 14 => 'ccaaaa', 15 => 'dcaaaa', 16 => 'ecaaaa', 17 => 'fcaaaa', 18 => 'adaaaa', 19 => 'bdaaaa', 20 => 'cdaaaa', 21 => 'ddaaaa', 22 => 'edaaaa', 23 => 'fdaaaa', 24 => 'aeaaaa', 25 => 'beaaaa', 26 => 'ceaaaa', 27 => 'deaaaa', 28 => 'eeaaaa', 29 => 'feaaaa', 30 => 'afaaaa', 31 => 'bfaaaa', 32 => 'cfaaaa', 33 => 'dfaaaa', 34 => 'efaaaa', 35 => 'ffaaaa', 36 => 'aabaaa', 37 => 'babaaa', 38 => 'cabaaa', 39 => 'dabaaa', 40 => 'eabaaa', 41 => 'fabaaa', 42 => 'abbaaa', 43 => 'bbbaaa', 44 => 'cbbaaa', 45 => 'dbbaaa', 46 => 'ebbaaa', 47 => 'fbbaaa', 48 => 'acbaaa', 49 => 'bcbaaa', 50 => 'ccbaaa', 51 => 'dcbaaa', 52 => 'ecbaaa', 53 => 'fcbaaa', 54 => 'adbaaa', 55 => 'bdbaaa', 56 => 'cdbaaa', 57 => 'ddbaaa', 58 => 'edbaaa', 59 => 'fdbaaa', 60 => 'aebaaa', 61 => 'bebaaa', 62 => 'cebaaa', 63 => 'debaaa', 64 => 'eebaaa', 65 => 'febaaa', 66 => 'afbaaa', 67 => 'bfbaaa', 68 => 'cfbaaa', 69 => 'dfbaaa', 70 => 'efbaaa', 71 => 'ffbaaa', 72 => 'aacaaa', 73 => 'bacaaa', 74 => 'cacaaa', 75 => 'dacaaa', 76 => 'eacaaa', 77 => 'facaaa', 78 => 'abcaaa', 79 => 'bbcaaa', 80 => 'cbcaaa', 81 => 'dbcaaa', 82 => 'ebcaaa', 83 => 'fbcaaa', 84 => 'accaaa', 85 => 'bccaaa', 86 => 'cccaaa', 87 => 'dccaaa', 88 => 'eccaaa', 89 => 'fccaaa', 90 => 'adcaaa', 91 => 'bdcaaa', 92 => 'cdcaaa', 93 => 'ddcaaa', 94 => 'edcaaa', 95 => 'fdcaaa', 96 => 'aecaaa', ～ （重いので）中略 ～ 46643 => 'fdffff', 46644 => 'aeffff', 46645 => 'beffff', 46646 => 'ceffff', 46647 => 'deffff', 46648 => 'eeffff', 46649 => 'feffff', 46650 => 'afffff', 46651 => 'bfffff', 46652 => 'cfffff', 46653 => 'dfffff', 46654 => 'efffff', 46655 => 'ffffff', )
添字が46655番 = 全部で46656個 = 6の6乗個。
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