data_structures_hw3/RecursiveMethods.java

// The RecursiveMethods class that implements several recursive solutions
// Your name here

public class RecursiveMethods {
    // This method calls the sumSquareRec method and returns the sum of the
    // squares of the elements in the array.
    public int sumSquares(int[] A) {
        // Do not make any changes to this method!
        return sumSquaresRec(A, 0);
    }

    // This method takes an integer array as well as an integer (the starting
    // index) and returns the sum of the squares of the elements in the array.
    public int sumSquaresRec(int[] A, int pos) {

        int current_int = A[pos];
        if (pos + 1 == A.length)
            return current_int * current_int;
        return current_int * current_int + sumSquaresRec(A, pos + 1);
    }

    // This method takes a character stack and converts all lower case letters
    // to upper case ones.
    public void upperStackRec(CharStack s) {
        if (s.isEmpty())
            return;
        else {
            char top = Character.toUpperCase(s.pop());
            upperStackRec(s);
            s.push(top);
        }
    }

    // This method reads a string and returns the string in the reversed order.
    public String reverseStringRec(String s) {

        if (s.equals(""))
            return s;
        return reverseStringRec(s.substring(1)) + s.substring(0, 1);

    }

    // This method takes a reference to the head of a linked list.
    // It returns the reference to the head of the linked list in the reversed order.
    public LNode reverseListRec(LNode head) {
        if (head == null)
            return head;
        if (head.getLink() == null)
            return head;

        LNode holder = reverseListRec(head.getLink());
        LNode next = head.getLink();

        next.setLink(head);
        head.setLink(null);
        return holder;

    }
}