Question

Consider the following recursive method in Java

public static int mystery(int n)

{

  if (n == 0)

  return 1;

   else   

return 4 * mystery (n - 1);  

}

What is the output of  mystery (3) using the code segment above

Show your work on your trace file

Answer 1

Step1

mystery (3) 3 is passed to mystery() method

public static int mystery(int n) n store the value 3 n = 3

{

  if (n == 0) n value is not 0, False execute else part

  return 1;

   else   

return 4 * mystery (n - 1); 4 * mystery(3-1) ===> 4 * mystery(2), again calling mystery() method, passing 2

}

Step2

public static int mystery(int n) n store the value 2, n = 2

{

  if (n == 0) n value is not 0, False execute else part

  return 1;

   else   

return 4 * mystery (n - 1); 4 * mystery(2-1) ===> 4 * mystery(1), again calling mystery() method, passing 1

}

Step3

public static int mystery(int n) n store the value 1, n = 1

{

  if (n == 0) n value is not 0, False execute else part

  return 1;

   else   

return 4 * mystery (n - 1); 4 * mystery(1-1) ===> 4 * mystery(0), again calling mystery() method, passing 0

}

Step4

public static int mystery(int n) n store the value 0, n = 0

{

  if (n == 0) n value is 0, True execute if block part

  return 1; return 1 to step3 mystery(0)

   else   

}

4 * mystery(0);

= 4 * 1

4 return to step2 mystery(1)

4 * mystery(1)

= 4 * 4

16 return to step1 mystery(2)

4 * mystery(2)

4 * 16

= 64

NOTE: If you have any doubt, please let me know through comments; I will surely revert back to you.

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