// Allison Obourn 
// CSE 143 - lecture 10
// Recursion practice and examples

import java.io.*;

public class Recursion {
   public static void main(String[] args) {
      System.out.println(pow(3, 4));
      System.out.println(pow(2, 0));

      System.out.println();
      printBinary(7); // 111
      System.out.println();
      printBinary(12); // 1100
      System.out.println();
      printBinary(42); // 101010
      System.out.println();
      
      crawl(new File("../.."));
   }

   // Returns the result of raising the base to the specified exponent.
   // pre: exp >= 0, throws IllegalArgumentException otherwise
   public static int pow(int base, int exp) {
      if (exp < 0) {
         throw new IllegalArgumentException();
      } else if(exp == 0) {
         return 1;
      } else if (exp % 2 == 0) {
         return pow(base * base, exp / 2);
      } else {
         // 2^1 = 2 = 2
         // 2^2 = 4 = 2 * 2
         // 2^3 = 8 = 2 * 2 * 2
         // 2^4 = 16 = 2 * 2 * 2 * 2 = 2 * 2^3
         return base * pow(base, exp - 1);
      }
   }

   // Prints the given decimal value in binary
   // pre: decimal >= 0
   public static void printBinary(int decimal) {
      if(decimal < 2) {
         System.out.print(decimal);
      } else {
         int last = decimal % 2;
         int rest = decimal / 2;
         
         printBinary(rest);
         printBinary(last);
      }
   }
   
   // Prints information about this file,
   // and (if it is a directory) any files inside it.
   public static void crawl(File f) {
      crawl(f, "");
   }
   
   // Prints the name of the given file at the specified level of indentation.
   // If the file is a directory, prints its content.
   // pre: the file exists
   private static void crawl(File f, String indent) {
      System.out.println(indent + f.getName());
      if(f.isDirectory()) {
         File[] files = f.listFiles();
         for(int i = 0; i < files.length; i++) {
            crawl(files[i], "    " + indent);
         }
      }
   }
}