feat: Refactor palindrome.clj for improved performance

otus-02/src/otus_02/homework/palindrome.clj

@@ -1,13 +1,30 @@
 (ns otus-02.homework.palindrome
   (:require [clojure.string :as string]))
 
-(def non-alphanumeric-pattern #"\W+")
+(def alphanumeric-pattern #"[a-zA-Z0-9\p{IsIdeographic}]")
 
-(defn normalize-string [^String input]
-  (-> input
-      string/lower-case
-      (string/replace non-alphanumeric-pattern "")))
+(defn alphanumeric? [c]
+  (boolean (re-matches alphanumeric-pattern (str c))))
+
+(defn normalize-char [c]
+  (string/lower-case (str c)))
 
 (defn is-palindrome [^String input]
-  (let [normalized-input (normalize-string input)]
-    (= normalized-input (string/reverse normalized-input))))
+  (let [length (.length input)]
+    (loop [left 0
+           right (dec length)]
+      (cond
+        (>= left right) true
+
+        (not (alphanumeric? (.charAt input left)))
+        (recur (inc left) right)
+
+        (not (alphanumeric? (.charAt input right)))
+        (recur left (dec right))
+
+        :else
+        (let [left-char (normalize-char (.charAt input left))
+              right-char (normalize-char (.charAt input right))]
+          (if (= left-char right-char)
+            (recur (inc left) (dec right))
+            false))))))