valid palindrome solution

Author: yhkee0404

valid-palindrome/yhkee0404.ts

@@ -0,0 +1,19 @@
+function isPalindrome(s: string): boolean {
+    const isAlpha = x => x.toLowerCase() >= 'a' && x.toLowerCase() <= 'z';
+    const isNumeric = x => x >= '0' && x <= '9';
+    const isAlphanumeric = x => isAlpha(x) || isNumeric(x);
+    let i = 0, j = s.length - 1;
+    while (i < j) {
+        while (i !== j && ! isAlphanumeric(s[i])) {
+            i++;
+        }
+        while (i !== j && ! isAlphanumeric(s[j])) {
+            j--;
+        }
+        if (s[i].toLowerCase() !== s[j].toLowerCase()) {
+            return false;
+        }
+        i++, j--;
+    }
+    return true;
+};