solve: valid-palindrome

Author: ready-oun

valid-palindrome/ready-oun.java

@@ -0,0 +1,48 @@
+class Solution {
+    public boolean isPalindrome(String s) {
+        StringBuilder cleaned = new StringBuilder(); 
+
+        for (char c : s.toCharArray()) {
+            if (Character.isLetterOrDigit(c)) {
+                cleaned.append(Character.toLowerCase(c)); 
+            }
+        }
+
+        int left = 0; 
+        int right = cleaned.length() - 1; 
+        while (left < right) {
+            // Fail fast: return false as soon as a mismatch is found
+            if (cleaned.charAt(left) != cleaned.charAt(right)) {
+                return false; 
+            }
+            left++;
+            right--; 
+        }
+
+        return true; 
+    }
+}
+
+/**
+converting all uppercase letters into lowercase letters
+removing all non-alphanumeric char
+
+1. cleaning 
+    0. str -> char with for-each loop  
+    1. check char if isLetterOrDigit
+    2. make char to LowerCase 
+    * Character Class static method 
+2. two ptrs comparison while left < right 
+    s[i] == s[n - 1 - i] 
+
+- Time: O(n) 
+
+ /** REMEMBER 
+1. length vs length() 
+
+arr.length => field 
+String(Builder).length() => method 
+
+2. “fail fast” approach: 
+As soon as we detect something wrong, we exit early.
+  */