feat: Add valid palindrome solution

Author: river20s

valid-palindrome/river20s.py

@@ -0,0 +1,7 @@
+import re
+
+class Solution(object):
+    def isPalindrome(self, s):
+        s = s.lower()
+        s = re.sub(r'[^a-z0-9]', '', s)
+        return s == s[::-1]