K. Redmyer - 2 months ago 12

PHP Question

I have been racking my brain at this for a few days and I seem to be stuck. I'm new to PHP so please forgive any sloppiness or errors.

Given a pattern, for example something like an email address "ab@?b?.ca" I need to replace any instance of '?' with all possible permutations from a set of characters 'a-e', '@', and '.'

This is what I have right now:

`function permute($str, $ch, $i, $n, &$output) {`

if ($i == $n) {

array_push($output, $str);

} else {

for ($x = $i; $x < $n; $x++) {

for ($y = 0; $y < count($ch); $y++) {

$str[$x] = $ch[$y];

permute($str, $ch, $i + 1, $n, $output);

}

}

}

}

# each ? in the pattern to be replaced by all possible permutations of characters in chars array

# a through e as well as @ and .

$output = array();

$chars = range('a', 'e');

array_push($chars, '@');

array_push($chars, '.');

# the pattern to be checked

$pattern = "ab@?b?.ca";

permute($pattern, $chars, 0, strlen($pattern), $output);

... which is very close to what I want, but not quite correct. The function operates on every character of the string, but it should only do the work on the '?'s. Is there something else I can do that I'm missing? I will respond in a comment and edit if I figure this out!

Answer

Here is my working solution:

```
function permute($str, $arr, $i, $n, &$result) {
$nLen = strlen($n);
// cycle through every position of needle
while (($i = strpos($str, $n, $i)) !== false) {
$i = $i + $nLen;
// cycle through each replacement value
foreach ($arr as $value) {
$modified = substr_replace($str, $value, $i - $nLen, $nLen);
// if there are no needles left, save it
if (stristr($modified, $n) === false) {
$result[] = $modified;
}
permute($modified, $arr, $i, $n, $result);
}
}
}
# each ? in the pattern to be replaced by all possible permutations of characters in chars array
# a through e as well as @ and .
$chars = range('a', 'e');
array_push($chars, '@');
array_push($chars, '.');
# the pattern to be checked
$pattern = "ab@?b?.ca";
$result = array();
$needle = '?';
$index = 0;
permute($pattern, $chars, $index, $needle, $result);
var_dump($result);
```

This assumes that you only want to save values in which no needles remain. For example, instead of:

```
array(63) {
[0]=>
string(9) "ab@ab?.ca"
[1]=>
string(9) "ab@aba.ca"
[2]=>
string(9) "ab@abb.ca"
// etc...
```

It will output:

```
array(49) {
[0]=>
string(9) "ab@aba.ca"
[1]=>
string(9) "ab@abb.ca"
[2]=>
string(9) "ab@abc.ca"
// etc...
```

If you do in fact want the first result, then simply remove the `stristr($modified, $n) === false`

conditional.