add valid-palindrome solution

Author: nakjun12

valid-palindrome/nakjun12.ts

@@ -0,0 +1,11 @@
+function isPalindrome(s: string): boolean {
+  const convertWord = s.toLowerCase().match(/[a-z0-9]/g) ?? [];
+  const length = convertWord.length;
+  for (let i = 0; i < length / 2; i++) {
+    if (convertWord[i] !== convertWord[length - 1 - i]) {
+      return false;
+    }
+  }
+
+  return true;
+}