Merge pull request neetcode-gh#1411 from brentonjackson/patch-1

Ahmad-A0 · web-flow · commit bc0870a2f60d · 2022-11-05T21:13:32.000Z
Update 125-Valid-Palindrome.js
diff --git a/javascript/125-Valid-Palindrome.js b/javascript/125-Valid-Palindrome.js
@@ -31,47 +31,27 @@ const reverse = (s) => s
  * @return {boolean}
  */
 var isPalindrome = function(s) {
-    if (!s.length) return true;
-
-    return isValid(s);/* Time O(N) */
-};
-
-const isValid = (s) => {
-    let [ left, right ] =  [ 0, (s.length - 1) ];
-
-    while (left < right) {                          /* Time O(N) */
-        [ left, right ] = moveToMid(s, left, right);/* Time O(N) */
-
-        const [ leftCode, rightCode ] = getCodes(s, left, right);
-  
-        const isEqual = leftCode === rightCode;
-        if (!isEqual) return false;
-
-        left++; right--;
+    if (s.length <= 1) return true;
+    
+    let [left, right] = [0, s.length - 1];
+    let leftChar, rightChar;
+    while (left < right) {
+        leftChar = s[left];
+        rightChar = s[right];
+        
+        // skip char if non-alphanumeric
+        if (!/[a-zA-Z0-9]/.test(leftChar)) {
+            left++;
+        } else if (!/[a-zA-Z0-9]/.test(rightChar)) {
+            right--;
+        } else {
+            // compare letters
+            if (leftChar.toLowerCase() != rightChar.toLowerCase()) {
+                return false;
+            }
+            left++;
+            right--;
+        }
     }
-
     return true;
-}
-
-const moveToMid = (s, left, right) => {
-    while ((left < right) && !isAlphaNumeric(s[left])) left++;  /* Time O(N) */
-    while ((left < right) && !isAlphaNumeric(s[right])) right--;/* Time O(N) */
-    
-    return [ left, right ];
-}
-
-const getCodes = (s, left, right) => [ getCode(s[left]), getCode(s[right]) ];
-
-const getCode = (char) => char.toLowerCase().charCodeAt(0);
-
-const isAlphaNumeric = (char) => {
-    const code = getCode(char);
-    
-    const [ a, z ] = [ 97, 122 ];
-    const isAlpha = (a <= code) && (code <= z);
-
-    const [ zero, nine ] = [ 48, 57 ];
-    const isNumeric = (zero <= code) && (code <= nine);
-
-    return isAlpha || isNumeric;
 };
