// 문자열의 길이구하기
public class Recursion5 {
    public static void main(String[] args) {
        int result = length("hello world");
        System.out.println("result : " + result);
    }

    public static int length(String str) {
        if (str.equals(""))
            return 0;
        return 1 + length(str.substring(1));
    }
}
//result
11

// 문자열 프린트
public class Recursion6 {
    public static void main(String[] args) {
        String str = "hello world";
        printChars(str);
    }

    public static void printChars(String str) {
        if (str.length() == 0)
            return;
        System.out.print(str.charAt(0));
        printChars(str.substring(1));
    }
}
//result
hello world

//배열의 합
public class Recursion7 {
    public static void main(String[] args) {
        int [] data = {1, 3, 4, 5,6};
        int result = sum(5, data);
        System.out.println("result is " + result);
    }

    public static int sum(int n, int [] data) {
        if (n <= 0)
            return 0;
        return sum(n - 1, data) + data[n - 1];
    }
}
//result
19