Question

**** All these methods should be implemented using RECURSIVE solutions (no looping statements)

// Java

// 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.

// This method uses recursion.
public int sumSquaresRec(int[] A, int pos)
{
// TODO: implement this method
      
return -1; // replace this statement with your own return
}   

// This method takes a character stack and converts all lower case letters
// to upper case ones.
public void upperStackRec(CharStack s)
{
// TODO: implement this method
}
  
// This method reads a string and returns the string in the reversed order.
public String reverseStringRec(String s)
{
// TODO: implement this method
      
return "dummy string"; // replace this statement with your own return
}
  
// This method takes as parameters a reference to the head of a linked list, a
// position specified by n, and a key. It returns the number of occurrences
// of the key in the linked list beginning at the n-th node. If n = 0, it means
// you should search in the entire linked list. If n = 1, then you should skip
// the first node in the list.
public int numOccurrencesRec(LNode node, int n, int key)
{
// TODO: implement this method
      
return -1; // replace this statement with your own return   
}
}

Answer 1

    // Java

    // 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.
    // This method uses recursion.
    public int sumSquaresRec(int[] A, int pos) {
        if(pos >= A.length) {
            return 0;
        }

        return A[0] * A[0] + 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()) {
            char c = Character.toUpperCase(s.pop());
            upperStackRec(s);
            s.push(c);
        }
    }

    // This method reads a string and returns the string in the reversed order.
    public String reverseStringRec(String s) {
        if(s.length() <= 1) {
            return s;
        }

        return reverseStringRec(s.substring(1)) + s.charAt(0);
    }

    // This method takes as parameters a reference to the head of a linked list, a
    // position specified by n, and a key. It returns the number of occurrences
    // of the key in the linked list beginning at the n-th node. If n = 0, it means
    // you should search in the entire linked list. If n = 1, then you should skip
    // the first node in the list.
    public int numOccurrencesRec(LNode node, int n, int key) {
        int count = 0;
        if(node == null) {
            return count;
        }
        if(n <= 0 && node.value == key) {
            count++;
        }
        return count + numOccurrencesRec(node.next, n-1, key);
    }

**************************************************

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