Valid Palindrome solution

Author: kim-young

valid-palindrome/kimyoung.js

@@ -0,0 +1,23 @@
+var isPalindrome = function (s) {
+    let left = 0, right = s.length - 1;
+    while (left < right) {
+        while (left < right && !isAlphaNumeric(s[left])) { // increment the left index until it's an alphanumeric character
+            left++;
+        }
+        while (left < right && !isAlphaNumeric(s[right])) { // decrement the right index until it's an alphanumeric character
+            right--;
+        }
+        if (s[left++].toLowerCase() !== s[right--].toLowerCase()) return false; // compare the two string values, if different return false;
+    }
+    return true;
+};
+
+function isAlphaNumeric(char) { // use ASCII code to findout if char is alphanumeric or not
+    const asciiCode = char.charCodeAt(0);
+    return (asciiCode >= 65 && asciiCode <= 90) ||
+        (asciiCode >= 97 && asciiCode <= 122) ||
+        (asciiCode >= 48 && asciiCode <= 57)
+}
+
+// time - O(n) iterate through the string once
+// space - O(1) no extra space created