Question

Consider the following definition of a recursive method. public static int mystery(int[] list, int first, int last) { if (first == last) return list[first]; else return list[first] + mystery(list, first + 1, last); } Given the declaration int[] alpha = {1, 4, 5, 8, 9}; What is the output of the following statement? System.out.println(mystery(alpha, 0, 4)); a. 1 b. 18 c. 27 d. 32

Answer 1

Answer:

c. 27

Explanation:

• In recursion method, a method calls itself until a condition becomes true and returned back. In mystery(), at first time, first is 0 and last is 4. Condition is checked and 0!=4 so else part is executed in which again mystery is called with first as 1 and last 4. This will go again and again until first=4.
• When first=4 it is also equal to last so if part is executed and alpha[4] is returned which is 9, now it comes alpha[3] +9 which is 8+9 =17 .
• It is returning values to its previous calls that is why it will reduce to alpha[0]+alpha[1]+alpha[2]+17 which is nothing but sum of all elements of a alpha
• Then, 1+4+5+8+9=27.