diff --git a/125.valid-palindrome.java b/125.valid-palindrome.java
index 147f21c..06c6d7a 100644
--- a/125.valid-palindrome.java
+++ b/125.valid-palindrome.java
@@ -16,24 +16,33 @@ class Solution {
             while(i<j && !isAlphanumberic(s.charAt(j))) {
                 j--;
             }
-            if(i==j) {
+            if(i>=j) {
                 break;
             }
             if(!isSameLeterIgnoreCase(s.charAt(i), s.charAt(j))) {
                 r = false;
                 break;
             }
+            i++;
+            j--;
         }
         return r;
     }
 
     private boolean isAlphanumberic(char c) {
-        return c >= 'a' && c <= 'z' || 
-        c >= 'A' && c <= 'Z' || c >='0' && c <= '9';
+        return isAlpha(c) || isNumberic(c);
+    }
+    
+    private boolean isAlpha(char c) {
+        return c >= 'a' && c <= 'z' || c >= 'A' && c <= 'Z';
+    }
+
+    private boolean isNumberic(char c) {
+        return c >= '0' && c <= '9';
     }
 
     private boolean isSameLeterIgnoreCase(char a, char b) {
-        return a == b || a - b == 'z' - 'a' || a - b == 'a' - 'z';
+        return isNumberic(a) && a == b || isAlpha(a) && isAlpha(b) && Character.toLowerCase(a) == Character.toLowerCase(b);
     }
 }
 // @lc code=end