add: valid-palindrome

Author: Yongseok-Choi-dev

valid-palindrome/YoungSeok-Choi.java

@@ -0,0 +1,31 @@
+
+// NOTE: 팰린드롬은 알파벳 소문자와 "숫자" 까지 포함하는듯 하다.
+// O(n) 알고리즘.
+import java.util.stream.Collectors;
+
+class Solution {
+    public boolean isPalindrome(String s) {
+
+        String filtered = s.chars()
+        .filter(Character::isLetterOrDigit)
+        .mapToObj(c -> String.valueOf((char) c))
+        .map(String::toLowerCase)
+        .collect(Collectors.joining());
+
+        char[] cArr = filtered.toCharArray();
+
+        int startIdx = 0;
+        int endIdx = cArr.length - 1;
+    
+        while(startIdx < endIdx) {
+            if(cArr[startIdx] != cArr[endIdx]) {
+                return false;
+            }
+            
+            startIdx++;
+            endIdx--;
+        }
+
+        return true;
+    }
+}