add: #220 Valid Palindrome

Author: sukyoungshin

valid-palindrome/sukyoungshin.ts

@@ -0,0 +1,24 @@
+const alphaNumSet = new Set([..."abcdefghijklmnopqrstuvwxyz0123456789"]);
+
+function isPalindrome(s: string): boolean {
+  let normalized = "";
+
+  for (const characters of s) {
+    const lower = characters.toLowerCase();
+    if (alphaNumSet.has(lower)) {
+      normalized += lower;
+    }
+  }
+
+  let left = 0;
+  let right = normalized.length - 1;
+  while (left < right) {
+    if (normalized[left] !== normalized[right]) {
+      return false;
+    }
+    left++;
+    right--;
+  }
+
+  return true;
+}