编辑代码

public class Main {
    public static boolean isPalindrome(String str) {
        return isPalindromeHelper(str, 0, str.length() - 1);
    }
    
    public static boolean isPalindromeHelper(String str, int start, int end) {
        if (start >= end) {
            return true;
        }
        
        if (str.charAt(start) != str.charAt(end)) {
            return false;
        }
        
        return isPalindromeHelper(str, start + 1, end - 1);
    }
    
    public static void main(String[] args) {
        String str = "level";
        System.out.println(isPalindrome(str)); // 输出true
        
        str = "hello";
        System.out.println(isPalindrome(str)); // 输出false
    }
}