add: valid-palindrome solution

Author: JEONGBEOMKO

valid-palindrome/JEONGBEOMKO.java

@@ -0,0 +1,32 @@
+class Solution {
+
+    /*
+    time complexity: O(n)
+    space complexity: O(n)
+     */
+
+    public boolean isPalindrome(String s) {
+
+        int left = 0;
+        int right = s.length() - 1;
+
+        while (left < right) {
+            while (left < right && !Character.isLetterOrDigit(s.charAt(left))) {
+                left++;
+            }
+
+            while (left < right && !Character.isLetterOrDigit(s.charAt(right))) {
+                right--;
+            }
+
+            if (Character.toLowerCase(s.charAt(left)) != Character.toLowerCase(s.charAt(right))) {
+                return false;
+            }
+
+            left++;
+            right--;
+            
+        }
+        return true;
+    }
+}