// This file contains several examples of recursive definitions.

import java.io.*;
import java.util.*;

public class Recurse2 {
    public static void main(String[] args) {
        System.out.println(stutter(-348));
        System.out.print("Binary representation of -39 = ");
        writeBinary(-39);
        System.out.println();
        int[] data = {3, 9, 15, 7};
        for (int i = 0; i <= data.length; i++) {
            int[] test = Arrays.copyOf(data, i);
            System.out.println("sum of " + Arrays.toString(test) + " = "
                               + sum(test));
        }
    }

    // returns the integer obtained by replacing every digit of n with two of
    // that digit.  For example, stutter(348) returns 334488.
    public static int stutter(int n) {
        if (n < 0) {
            return -stutter(-n);
        } else if (n < 10) {
            return n * 11;
        } else {
            return 100 * stutter(n / 10) + stutter(n % 10);
        }
    }

    // writes the binary representation of n to System.out
    public static void writeBinary(int n) {
        if (n < 0) {
            System.out.print("-");
            writeBinary(-n);
        } else if (n < 2) {
            System.out.print(n);
        } else {
            writeBinary(n / 2);
            System.out.print(n % 2);
        }
    }

    // returns the sum of the numbers in the given array
    public static int sum(int[] list) {
        return sum(list, 0);
    }

    // computes the sum of the list starting at the given index
    private static int sum(int[] list, int index) {
        if (index == list.length) {
            return 0;
        } else {
            return list[index] + sum(list, index + 1);
        }
    }
}