Valid Palindrome

Author: TonyKim9401

valid-palindrome/TonyKim9401.java

@@ -0,0 +1,37 @@
+// TC: O(n)
+// SC: O(n)
+class Solution {
+    public boolean isPalindrome(String s) {
+        String target = checkString(s);
+        return checkPalindrome(target);
+    }
+
+    private String checkString(String s) {
+        StringBuilder sb = new StringBuilder();
+        for (char c : s.toCharArray()) {
+            if (c >= 'a' && c <= 'z') {
+                sb.append(c);
+            }
+            if (c >= 'A' && c <= 'Z') {
+                c = (char)(c - 'A' + 'a');
+                sb.append(c);
+            }
+            if (c >= '0' && c <= '9') {
+                sb.append(c);
+            }
+        }
+        return sb.toString();
+    }
+
+    private Boolean checkPalindrome(String target) {
+        int start = 0;
+        int end = target.length() - 1;
+
+        while (start < end) {
+            if (target.charAt(start) != target.charAt(end)) return false;
+            start += 1;
+            end -= 1;
+        }
+        return true;
+    }
+}