编辑代码

public class Main {
    public static void main(String[] args) {
        String str = "level";
        String str2 = "1level";
        String str3 = "";
        System.out.println(recursiveEcho(str));
        System.out.println(recursiveEcho(str2));
        System.out.println(recursiveEcho(str3));
        System.out.println("\n"+iterativeEcho(str));
        System.out.println(iterativeEcho(str2));
        System.out.println(iterativeEcho(str3));
    }

    public static boolean recursiveEcho(String str) {
        if (str.length() <= 1) {
            return true;
        } else {
            char firstChar = str.charAt(0);
            char lastChar = str.charAt(str.length() - 1);
            if (firstChar == lastChar) {
                String subStr = str.substring(1, str.length() - 1);
                return recursiveEcho(subStr);
            } else {
                return false;
            }
        }
    }

    public static boolean iterativeEcho(String str) {
        int left = 0;
        int right = str.length() - 1;
        while (left < right) {
            if (str.charAt(left) != str.charAt(right)) {
                return false;
            }
            left++;
            right--;
        }
        return true;
    }
}