Thread: Recursion Guidance

So my professor assigned two problems to the class yesterday to be done recursively:

The first is to find the maximum number in an array. We had predefined methods and a tester, all we had to do was fill in the methods for the class DataSet. This problem appears to work correctly but I would like to know if there is anything wrong with the way that I implemented it for the purpose of doing it using recursion.

Tester

/**
* A tester class for the recursive maximum
*/
public class DataTester {
	public static void main (String[] args) {
		int[]values = {1, 10, 100, -1, -10, -100, 100, 0};
 
		//OTHER TESTING VALUES
		//int[]values = {2, 5, 6, 3, 1};
		//int[]values = {9, 8, 7, 6, 5};
		//int[]values = {9, 2, 4, 9, 0};
 
		DataSet data = new DataSet (values, 0, values.length -1);
		System.out.println("Max :: " + data.getMaximum());
		System.out.println("Expected :: 100");
	}
}

Implementation

 
public class DataSet {
	private int[] values;
	private int first;
	private int last;
 
	/**
	 * Constructor that will set the array values, and where the array begins and ends
	 * @param values
	 * @param first
	 * @param last
	 */
	public DataSet (int[] values, int first, int last) {
		this.values = values;
		this.first = first;
		this.last= last;
	}
 
	/**
	 * This finds the maximum values in an array using recursion
	 * @return
	 */
	public int getMaximum() {
 
		//BASE LINE
		if (first == last) { return values[first]; }
 
		else if (first < last) {
			DataSet d = new DataSet(values, first, last-1);
			int temp = d.getMaximum();
			if (temp > values[last]) {return temp; }
			else {return values[last]; }
		}
 
		return first;
	}
}

The second problem is to find the number of handshakes that will be made if each person in a room shakes hands with each other person exactly one time. So if two people were in the room, there would be a total of 1 handshake.

I have this working but I'm pretty sure that my implementation is incorrect because I have my handshakes variable as an instance variable. I'm pretty sure that it should be within my "getNumHandshakes()" method but I can't seem to get correct results when I do it that way.

Tester

 
public class RoomTester {
	public static void main (String [] args) {
		Room a = new Room(0);
		System.out.println("A :: People :: 0 :: HandShakes :: " + a.getNumHandshakes() + " :: Expected :: 0");
 
		Room b = new Room(1);
		System.out.println("B :: People :: 1 :: HandShakes :: " + b.getNumHandshakes() + " :: Expected :: 0");
 
		Room c = new Room(2);
		System.out.println("C :: People :: 2 :: HandShakes :: " + c.getNumHandshakes() + " :: Expected :: 1");
 
		Room d = new Room(3);
		System.out.println("D :: People :: 3 :: HandShakes :: " + d.getNumHandshakes() + " :: Expected :: 3");
 
		Room e = new Room(4);
		System.out.println("E :: People :: 4 :: HandShakes :: " + e.getNumHandshakes() + " :: Expected :: 6");
 
		Room f = new Room(5);
		System.out.println("F :: People :: 5 :: HandShakes :: " + f.getNumHandshakes() + " :: Expected :: 10");
 
		Room g = new Room(6);
		System.out.println("G :: People :: 6 :: HandShakes :: " + g.getNumHandshakes() + " :: Expected :: 15");
	}
 
}

Implementation

 
public class Room {
	private int roomPeople = 0;
	private int handshakes = 0;
 
	public Room (int people) {
		roomPeople = people;
	}
 
	public Room() {
		roomPeople = 3;
	}
 
	public int getPeople() {
		return roomPeople;
	}
 
	public void setPeople (int p) {
		roomPeople = p;
	}
 
	public int getNumHandshakes() {
 
		//No people, no handshakes
		if (roomPeople == 0) {return 0;}
 
		//One person isn't going to shake their own hand
		else if (roomPeople == 1) {return 0;}
 
		//Two people = one handshake
		else if (roomPeople >= 2) {
			handshakes = handshakes + roomPeople-1;
			roomPeople--;
			getNumHandshakes();
 
			return (handshakes);
		}
		else { return -1234;	}
	}
}

I'm new to recursion and I can't seem to break myself of thinking iteratively because I want to do these using simple loops but alas that isn't the assignment.

Can you tell me in what direction I need to go to do the second problem correctly using recursion.
Also, any general tips on programming recursively would be very helpful.