Rabin Karp in PHP (#3005)

Rabin Karp in PHP

Rabin_Karp/Rabin_Karp.php

@@ -0,0 +1,63 @@
+// Rabin Karp Algorithm
+/*
+AN : range or No of alphabets
+val : AN ^ patlen-1
+patlen : pattern length
+PN: any prime no given input from main
+*/
+
+/* Time-Complexity:-
+The average case running time of the Rabin-Karp algorithm = O(n+m).
+The best case running time of the Rabin-Karp algorithm = O(n+m).
+The worst-case running time of the Rabin-Karp algorithm = O(nm).
+*/
+
+<?php
+
+$text = "XWINGO XOR WINGO";
+$pattern = "WINGO";
+$PN = 101;  // A prime number
+search($pattern, $text, $PN);
+
+function search($pattern, $text, $PN){
+    $patlen = strlen($pattern);    // pattern length
+    $txtlen = strlen($text);       // text length
+    $AN = 256;
+    $val = 1;
+    $hpat = 0;       // pattern hash value
+    $htxt = 0;       // text hash value
+    for($i = 0; $i < $patlen; $i++) {
+        $val = ($val * $AN) % $PN;
+    }
+    for($i = 0; $i < $patlen; $i++) {
+         $hpat = ($AN * $hpat + $pattern[$i]) % $PN;
+         $htxt = ($AN * $htxt + $text[$i]) % $PN;
+    }
+    for($i = 0; $i <= $txtlen - $patlen; $i++) {
+        if ($hpat == $htxt ){
+            // Check for patterns
+            for ($j = 0; $j < $patlen; $j++) {
+                if ($text[$i + $j] != $pattern[$j]) {
+                    break;
+                }
+            }
+            if ($j == $patlen) {
+                echo "Found at index starting from $i";
+            }
+        }
+        // Calculate the new pattern including i + m
+        $htxt = ($AN * ($htxt - $val * $text[$i]) + $text[$i + $patlen]) % $PN;
+        if($htxt < 0) {
+            $htxt = $htxt + $PN;
+        }
+    }
+}
+?>
+
+/*
+INPUT : XWINGO XOR WINGO
+        WINGO
+        101
+OUTPUT: Found at index starting from 1
+        Found at index starting from 11
+*/