// Zorah Fung, CSE 143
// This file contains several examples of recursive definitions.

import java.util.*;

public class Recursion {
    public static void main(String[] args) {
        System.out.print("Binary representation of 45703 = ");
        writeBinary(45703);
        System.out.println();
        System.out.println(isPalindrome("racecar"));
        System.out.println(isPalindrome("banana"));
        int[] data = {3, 9, 15, 7};
        for (int i = 0; i <= data.length; i++) {
            int[] test = Arrays.copyOfRange(data, data.length - i, data.length);
            System.out.println("sum of " + Arrays.toString(test) + " = "
                               + sum(test));
        }
    }

    // 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); // we could also call writeBinary(n % 2)
        }
    }

    // returns true if the given string is the same forwards as
    // backwards, false otherwise.
    public static boolean isPalindrome(String s) {
        if (s.length() <= 1) {
            return true;
        } else {
            char first = s.charAt(0);
            char last = s.charAt(s.length() - 1);
            String middle = s.substring(1, s.length() - 1);
            return first == last && isPalindrome(middle);       
        }
    } 

    // 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);
        }
    }
}