String compression in php - php

Question

Here is my input
aaaabbaaaababbbcccccccccccc
And this is my expected output
a4b2a4b1a1b3c12
I tried like doing foreach and then concating the count of values. It seems like brutforcing. Is there any way to do it efficiently in php .
Help pls

Answer 1

You can use regular expression to get the result
preg_match_all('/(.)\1*/', $str, $m, PREG_SET_ORDER);
$m = array_map(function($i) { return $i[1] . strlen($i[0]); } , $m);
echo implode('', $m); // a4b2a4b1a1b3c12
demo

Answer 2

Here's an example of how to do it with a few for loops (encoding and decoding):
$input = 'aaaabbaaaababbbcccccccccccc';
$encoded = SillyEncoding::encode($input);
$decoded = SillyEncoding::decode($encoded);
echo "input = \t", var_export($input, true), "\n";
echo "encoded = \t", var_export($encoded, true), "\n";
echo "decoded = \t", var_export($decoded, true), "\n";
Output:
input = 'aaaabbaaaababbbcccccccccccc'
encoded = 'a4b2a4b1a1b3c12'
decoded = 'aaaabbaaaababbbcccccccccccc'
The SillyEncoding class:
class SillyEncoding
{
private static $digits = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
static function encode($string)
{
$output = '';
if (strlen($string) > 0) {
$count = 0;
$char = $string[0];
for ($i = 0; isset($string[$i]); ++$i) {
if (isset(self::$digits[$string[$i]])) {
throw new \InvalidArgumentException(sprintf('The input string must not contain a digit at offset %d, got "%s"', $i, $string[$i]));
}
if ($string[$i] === $char) {
++$count;
} else {
$output .= "{$char}{$count}";
$count = 1;
$char = $string[$i];
}
if (!isset($string[$i + 1])) {
$output .= "{$char}{$count}";
}
}
}
return $output;
}
static function decode($string)
{
$output = '';
$length = strlen($string);
if ($length > 0) {
$char = $string[0];
$count = null;
if ($length < 2) {
throw new \InvalidArgumentException(sprintf('Input string must be empty or at least 2 bytes long, got %d bytes', $length));
}
if (isset(self::$digits[$string[0]])) {
throw new \InvalidArgumentException(sprintf('Input string must not start with a digit, got "%s"', $string[0]));
}
for ($i = 1; isset($string[$i]); ++$i) {
$isDigit = isset(self::$digits[$string[$i]]);
if ($isDigit) {
$count .= $string[$i];
}
if (!$isDigit || !isset($string[$i + 1])) {
if (null === $count) {
throw new \InvalidArgumentException(sprintf('Expected a digit at offset %d, got "%s"', $i, $string[$i]));
}
$count = (int) $count;
for ($j = 0; $j < $count; ++$j) {
$output .= $char;
}
$char = $string[$i];
$count = null;
}
}
}
return $output;
}
}
A few things to note:
this isn't an efficient compression algorithm - it might reduce the size if there are many repeated characters, but if you feed it "normal" text the output will be about twice the size of the input
the input cannot contain any digits whatsoever (OP: "the input will be strictly alphabets")

Answer 3

$str = str_split('aaaabbaaaababbbcccccccccccc');
$count = 0;
$a=$result=$b='';
for ($i=0; $i <= count($str); $i++) {
if($a==$str[$i]){
$count++;
$result = $a.$count;
} else{
if ($count > 0) {
$b .= $result;
}
$count = 1;
$a = $str[$i];
$result = $a.$count;
}
}
print_r($b);
See result