[HAI] week3 two pointer palindrome

https://leetcode.com/problems/valid-palindrome/description/

lib/isPalindrome/isPalindrome.ts

@@ -0,0 +1,30 @@
+function isLetter(c: string) {
+  if (/\d/.test(c)) return true;
+  return c.toLowerCase() != c.toUpperCase();
+
+}
+
+export function isPalindrome(s: string): boolean {
+  let L = 0;
+  let R = s.length - 1;
+
+  while (L <= R) {
+    let lChar = s[L].toLowerCase();
+    let rChar = s[R].toLowerCase();
+
+    if (!isLetter(lChar)) {
+      L++;
+      continue;
+    }
+    if (!isLetter(rChar)) {
+      R--;
+      continue;
+    }
+
+    if (lChar !== rChar) return false;
+    L++;
+    R--;
+  }
+
+  return true;
+};