2016 Update

Task/Inverted-index/PHP/inverted-index.php

@@ -0,0 +1,46 @@
+<?php
+
+function buildInvertedIndex($filenames)
+{
+    $invertedIndex = [];
+
+    foreach($filenames as $filename)
+    {
+        $data = file_get_contents($filename);
+
+        if($data === false) die('Unable to read file: ' . $filename);
+
+        preg_match_all('/(\w+)/', $data, $matches, PREG_SET_ORDER);
+
+        foreach($matches as $match)
+        {
+            $word = strtolower($match[0]);
+
+            if(!array_key_exists($word, $invertedIndex)) $invertedIndex[$word] = [];
+            if(!in_array($filename, $invertedIndex[$word], true)) $invertedIndex[$word][] = $filename;
+        }
+    }
+
+    return $invertedIndex;
+}
+
+function lookupWord($invertedIndex, $word)
+{
+    return array_key_exists($word, $invertedIndex) ? $invertedIndex[$word] : false;
+}
+
+$invertedIndex = buildInvertedIndex2(['file1.txt', 'file2.txt', 'file3.txt']);
+
+foreach(['cat', 'is', 'banana', 'it'] as $word)
+{
+    $matches = lookupWord($invertedIndex, $word);
+
+    if($matches !== false)
+    {
+        echo "Found the word \"$word\" in the following files: " . implode(', ', $matches) . "\n";
+    }
+    else
+    {
+        echo "Unable to find the word \"$word\" in the index\n";
+    }
+}