[염혜정] 2026/10/06

leetcode3/염혜정/125. Valid Palindrome.java

@@ -0,0 +1,29 @@
+// 투포인터
+// O(n)
+
+class Solution {
+    public boolean isPalindrome(String s) {
+        StringBuilder sb = new StringBuilder();
+        for (int i = 0; i<s.length(); i++) {
+            char c = Character.toLowerCase(s.charAt(i));
+            if (isLetter(c) || isNumber(c)) sb.append(c);
+        }
+
+        int left = 0;
+        int right = sb.length() -1;
+        while (left<right) {
+            if (sb.charAt(left) != sb.charAt(right)) return false;
+            left++;
+            right--;
+        }
+        return true;
+    }
+
+    boolean isLetter(int ord) {
+        return ord>=97 && ord <=122;
+    }
+
+    boolean isNumber(int ord) {
+        return ord>=48 && ord <=57;
+    }
+}