RecursionTest.java

/*
* this class demos recursive methods.
* @ Author: Maricel Vicente
*/
public class RecursionTest
{  
   /*
   * This function calcuated bunny years.
   * We have a number of bunnies and each bunny has two big floppy ears. 
   * We want to compute the total number of ears across all the bunnies recursively 
   * (without loops or multiplication).
   *
   *Example input/output:
   *bunnyEars(0) → 0
   *bunnyEars(1) → 2
   *bunnyEars(2) → 4
   *
   */
   public static int bunnyEars(int bunnies) 
   {
      //COMPLETE THIS
      // Base case: if bunnies==0, just return 0.
     if (bunnies == 0) {
       return 0;
     }
     // Recursive case: otherwise, make a recursive call with bunnies-1
     // (towards the base case), and fix up what it returns.
     else {
       return bunnies * bunnyEars(bunnies-1);
     }
     
     
    
   }
 
 
   
   /*
   * This method is a recursive method 
   *
   *Example input/output:
   *countA("anastasia") → 4
   *countA("bob") → 0
   *countA("") → 0
   *
   */
   public static int countA(String str) 
   {
      //COMPLETE THIS
      // Base case -- return simple answer
      
     if (str.length() == 0) {
       return 0;
     }
      
      // Deal with the very front of the string (index 0) -- count "A" there.
     int count = 0;
     if (str.substring(0, 1).equals("A")) {
       count = 1;
     }
     return count + countA(str.substring(1));
      
      // Make a recursive call to deal with the rest of string (the part beyond the front).
      // Add count to whatever the recursive call returns to make the final answer.
      // Note that str.substring(1) starts with char 1 and goes to the
      // end of the string.
     
     
     
   }
   
   
   
   
   /* 
   * The fibonacci sequence is a famous bit of mathematics, and it happens to have 
   * a recursive definition. The first two values in the sequence are 0 and 1 
   * (essentially 2 base cases). Each subsequent value is the sum of the previous two 
   * values, so the whole sequence is: 0, 1, 1, 2, 3, 5, 8, 13, 21 and so on. 
   * Define a recursive fibonacci(n) method that returns the nth fibonacci number, 
   * with n=0 representing the start of the sequence.
   *
   * fibonacci(0) → 0
   * fibonacci(1) → 1
   * fibonacci(2) → 1
   *
   */
   public static int fibonacci(int n) 
   {
      //COMPLETE THIS
      // No direction provided. Think and come up with a solution.
     if (n <= 1) {
       return n; 
     }
     else {
       return fibonacci(n-1) + fibonacci(n-2); 
     }
   }

   
   
   public static void main(String[] args)
   {
      //uncomment the following to test bunnyEars() method
      // System.out.println("bunnyEars(10) = " + bunnyEars(10)); // output should be 20
      
      //uncomment the following to test countA() method
      //System.out.println("countA(anastasia)" + " = " + countA("anastasia")); // output should be 4
      //System.out.println("countA()" + " = " + countA("")); // output should be 0
      
      //uncomment the following to test fibonacci() method
      //System.out.println("fibonacci(2) = " + fibonacci(2)); // output should be 1
      //System.out.println("fibonacci(9) = " + fibonacci(9)); // output should be 34


   }

   

}