Data commit

Task/LZW-compression/PHP/lzw-compression.php

@@ -0,0 +1,64 @@
+class LZW
+{
+    function compress($unc) {
+        $i;$c;$wc;
+        $w = "";
+        $dictionary = array();
+        $result = array();
+        $dictSize = 256;
+        for ($i = 0; $i < 256; $i += 1) {
+            $dictionary[chr($i)] = $i;
+        }
+        for ($i = 0; $i < strlen($unc); $i++) {
+            $c = $unc[$i];
+            $wc = $w.$c;
+            if (array_key_exists($w.$c, $dictionary)) {
+                $w = $w.$c;
+            } else {
+                array_push($result,$dictionary[$w]);
+                $dictionary[$wc] = $dictSize++;
+                $w = (string)$c;
+            }
+        }
+        if ($w !== "") {
+            array_push($result,$dictionary[$w]);
+        }
+        return implode(",",$result);
+    }
+
+    function decompress($com) {
+        $com = explode(",",$com);
+        $i;$w;$k;$result;
+        $dictionary = array();
+        $entry = "";
+        $dictSize = 256;
+        for ($i = 0; $i < 256; $i++) {
+            $dictionary[$i] = chr($i);
+        }
+        $w = chr($com[0]);
+        $result = $w;
+        for ($i = 1; $i < count($com);$i++) {
+            $k = $com[$i];
+            if (isset($dictionary[$k])) {
+                $entry = $dictionary[$k];
+            } else {
+                if ($k === $dictSize) {
+                    $entry = $w.$w[0];
+                } else {
+                    return null;
+                }
+            }
+            $result .= $entry;
+            $dictionary[$dictSize++] = $w . $entry[0];
+            $w = $entry;
+        }
+        return $result;
+    }
+}
+
+//How to use
+$str = 'TOBEORNOTTOBEORTOBEORNOT';
+$lzw = new LZW();
+$com = $lzw->compress($str);
+$dec = $lzw->decompress($com);
+echo $com . "<br>" . $dec;