Question

Rearrange the following lines of code to produce a recursive method: public static int sum(ArrayList a) which returns the sum of the elements in an ArrayList without using either a loop or a recursive helper method. Not all lines are useful.

a) Java coding
b) Python scripting
c) Recursive programming
d) Algorithmic design

Answer 1

To create the recursive method to sum elements of an ArrayList in Java, rearrange the code to call the method itself with a smaller list until reaching the base case. The sum function uses head recursion to calculate the total without loops or helper methods.

Step-by-step explanation:

The student is asking how to rearrange the code to create a recursive method to sum the elements of an ArrayList in Java without using loops or helper methods. To achieve this, arrange the code so that the method calls itself with a smaller subset of the ArrayList until the base case is reached, which is typically when the ArrayList size is 0. Here's how a possible implementation might look:

public static int sum(ArrayList<Integer> list) {
if(list.size() == 0)
return 0;
else
return list.remove(0) + sum(list);
}

This recursive method uses the concept of head recursion, where the method first calls itself with a smaller problem, and once reaching the base case, unwinds and computes the sum on the return path. Note that this approach modifies the original ArrayList by removing elements, which may not be desirable in all cases.