// CSE 143, Summer 2016
// This file contains several examples of recursive definitions.

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

public class Recurse2 {
  public static void main(String[] args) {
    // client to writeBinary
    writeBinary(384);

    // is Palindrome client code
    String[] words = {"madam", "racecar", "seastar", "java"};
    for (String s : words) {
      System.out.println(s + ": " + isPalindrome(s));
    }        
    System.out.println();

    // pow client code
    for (int i = 0; i < 5; i++) {
      System.out.println("2 to the power of " + i + ": " +
          pow(2, i));
    }
    System.out.println();

    // sum client code
    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));
    }
  }

  public static void writeBinary(int n) {
    if (n < 0) {
      System.out.print("-");
      writeBinary(-n);
    } else if (n / 2 == 0) {
      System.out.println(n);
    } else {
      writeBinary(n / 2);
      System.out.print(n % 2);
    }
  }

  // pre : given word is not null, throws a NullPointerException if it is null
  // returns true if the given word is a palindrome, false otherwise
  public static boolean isPalindrome(String word) {
    if (word.length() <= 1) {
      return true;
    } else {
      if (word.charAt(0) == word.charAt(word.length() - 1)) {
        return isPalindrome(word.substring(1, word.length() - 1));
      } else {
        return false;
      }
    }
  }

  // alternate solution to isPalindrome
  public static boolean isPalindrome2(String word) {
    if (word.length() < 2) {
      return true;
    } else {
      return word.endsWith("" + word.charAt(0)) && isPalindrome(word.substring(1, word.length() - 1));
    }
  }


  // returns the given base raised to the given exponent
  public static int pow(int base, int exp) {
    if (exp == 0) {
      return 1;
    } else {
      return base * pow(base, exp - 1);
    }
  }

  // pre : s != null
  // post: returns the sum of all elements in s
  public static int sum(Stack<Integer> s) {
    if (s.isEmpty()) {
      return 0;
    } else {
      int n = s.pop();
      int rest = sum(s);
      // remember to push n back!
      s.push(n);
      return n + rest;
    }
  }

  public static int sum(int[] list) {
    if (list == null) {
      throw new IllegalArgumentException();
    }
    return sum(list, 0);
  }

  // returns the sum of the numbers in the given array
  private static int sum(int[] list, int index) {
    if (index == list.length) {
      return 0;
    } else {
      return list[index] + sum(list, index + 1);
    }
  }
}