在PHP里其中一个Permutation方程式。
<?php
$c = \" ABCD\";
$n = 4;
$i = 0;
echo \"<pre>\";
for ($m1=1;$m1<=$n;$m1++) {
for ($m2=1;$m2<=$n;$m2++) {
if ($m1 == $m2) {
continue;
}
for ($m3=1;$m3<=$n;$m3++) {
if ($m1 == $m2 || $m2 == $m3 || $m3 == $m1) {
continue;
}
for ($m4=1;$m4<=$n;$m4++) {
if ($m1 == $m2 || $m1 == $m3 || $m1 == $m4 || $m2 == $m3 || $m2== $m4 || $m3 == $m4) {
continue;
}
$i++;
$out[$i] = $c[$m1].$c[$m2].$c[$m3].$c[$m4];
}
}
}
}
$out = array_unique($out);
print_r($out);
echo \"</pre>\";
?>
Array
(
[1] => ABCD
[2] => ABDC
[3] => ACBD
[4] => ACDB
[5] => ADBC
[6] => ADCB
[7] => BACD
[8] => BADC
[9] => BCAD
[10] => BCDA
[11] => BDAC
[12] => BDCA
[13] => CABD
[14] => CADB
[15] => CBAD
[16] => CBDA
[17] => CDAB
[18] => CDBA
[19] => DABC
[20] => DACB
[21] => DBAC
[22] => DBCA
[23] => DCAB
[24] => DCBA
)