feat: valid-palindrome solution

Author: sm9171

valid-palindrome/sm9171.java

@@ -0,0 +1,12 @@
+class Solution {
+    public boolean isPalindrome(String s) {
+        String str = s.toLowerCase().replaceAll("[^a-z0-9]","");
+        char[] charArray = str.toCharArray();
+        for (int i = 0; i < charArray.length / 2; i++) {
+            if (charArray[i] != charArray[charArray.length - i - 1]) {
+                return false;
+            }
+        }
+        return true;
+    }
+}