S307 - Final - Spring 2007

1. 2 points each. Big O answers with out the O() are okay.
A.    25		B. EMCOTUP
     /  \		C. CMOEUPT
   -5    39		D. COMPUTE
     \			E. No
     12			F. 935141
     /			G. O(NlogN)
    7

H. Must be able to test if an object is less than,
equal to or greater than objects already in the tree.
(Or words to that effect.) -1 if appropriate

I. 2^16

J. No, can't accept ArrayLists unless specifically
parameterize with String; ArrayList<anything other than String>
is a syntax error. -1 if appropriate
(Or words to that effect.)

K. O(K) accept O(K-N)

L. O(N)

M. Instance variable for the number of elements
(Or words to that effect.)

N. O(logN)

O. Unless the new encoding scheme is agreed upon, the key / new encoding scheme
must be sent as well and for small files that is a large amount of overhead (Or
words to that effect.)

2.
Special cases:
1. adding to empty list.
2. adding at position 0 in none empty list.

public boolean insert(Object item, int pos){
	boolean added = false;

	// empty list or position == 0?
	if( pos == 0){
		added = true;
		head = new Node(item, head)
	} else if(head != null) {

	    Node temp = head;
	    int moved = 0;

	    //try to move to the node before the position to insert at
	    while( moved < (pos -1) && temp.getNext() != null) {
	    	temp = temp.getNext();
	    	moved++:
	    }

	    //if able to get to correct spot, insert new node
	    if( moved == (pos - 1) ){
	    	added = true;
	    	temp.setNext( new Node(item, temp.getNext() );
	    }
	}

	return added;
}

Criteria:

empty case : 1 pt.
pos 0 case : 1 pt
general case
	temp node 2 pt
	move to correct position attempt : 3 pts
	move to correct position correct : 3 pts
	add new node if possible attempt: 2 pts
	add new node if possible correct: 2 pts
return result : 1 pts

3.
private int numIncorrectNodes(){
	return helper(root);
}

private int helper(TreeNode n){
	if( n == null )
		return 0;

	int numBad = 0;
	boolean left = true;
	if( n.getLeft() != null )
		left = n.getValue().compareTo( n.getLeft().getValue() ) > 0;

	boolean right = true;
	if( n.getRight() != null )
		right= n.getValue().compareTo( n.getRight().getValue() ) > 0;

	if( !(left && right )
		numBad++;

	return numBad +  helper(n.getLeft()) + helper(n.getRight());;
}

helper method : 2
base case : 5
current node check attenpt : 3
current node check correct : 4
recurse left and right check attempt : 2
recurse left and right check correct : 3
return : 1

4.
    private int numBadLinks(){
        int numBad = 0;
        
        //get an Iterator for the nodes
        Iterator<Integer> nodes = myLinks.keySet().iterator();

        while(nodes.hasNext()){

            	Iterator<Integer> links = myLinks.get(nodes.next).iterator();

            	while( links.hasNext() ){
            	    int currentlink = links.next();
            	    if( !myLinks.containsKey(currentLink) )
            	    	numBad++
                	else if(!myLinks.get(currentKey).contains(link.next))
                    	numBad++;
                    	
                    // could shorten this to
                    // if( !(myLinks.containsKey(currentLink) && myLinks.get(currentKey).contains(link.next) )
                    //     numBad++;
                    // must do the containsKey first or we'll get a NPE
                }
            }
        }
        return numBad;
    }

	//version to with enhanced for. Much simpler
    public int numBadLinks2(){
        int numBad = 0;
        //get an Iterator for the nodes


        for(int currentKey : myLinks.keySet() ){
            for(int link : myLinks.get(currentKey) ){
                if( !myLinks.containsKey(link) )
                	numBad++;
                else if(!myLinks.get(currentKey).contains(link))
                    numBad++;
            }
        }
        return numBad;
    }

iterate through keys attempt : 3
iterate through keys correct : 3
for a given key iterate through set attempt : 3
for a given key iterate through set correct : 3
for each key check if assoctiated link exists attempt : 3
for each key check if assoctiated link exists correct : 3
track num bad : 1
return num bad : 1

5.
// many to 1 answer
public boolean isSubset(Stack s, Queue q){
	boolean result = true;
	Stack tempStack = new Stack();
	Queue tempQueue = newQueue();

	//look for all items. Stop if no more or not a match
	while( result && !s.isEmpty ){
		tempStack.push(s.pop());

		//look for tempStack item
		boolean found = false
		while( !q.isEmpty() ){
			if it matches set found to true and keep it that way
			if( q.front().equals( tempStack.top() ) )
				found = true;
			tempQueue.enqueue( q.dequeue() );
		}
		assert q.isEmpty;
		result = found;

		//restore original queue
		while(! tempQueue.isEmpty() )
			q.enqueue( tempQueue() );
	}
	
	//restore stack
	while( !tempStack.isEmpty() )
		s.push(temStack.pop() );
		
	return result;
}

temp stacks and queues 1 pt
look for items attempt 3 pts
look for particular item attempt 3 pts
look for particular item correct 3 pts
restore stack 2 pts
restore  queue 2 pts
return result 1 pt
none queue / stack methods -3

// 1 to 1 answer
public boolean isSubset(Stack s, Queue q){
	boolean result = true;
	Stack tempStack = new Stack();
	Queue tempQueue = newQueue();

	//make a copy of the original queue
	int qSize = 0;
	Queue original = new Queue();
	while( !q.isEmpty() ){
		original.enqueue( q.dequeue );
		size++;
	}
	//copy back into q
	for(int i = 0; i < size; i++){
		q.enqueue( original.front() );
		original.enqueue( orginal.dequeue() );
	}

	while( result && !s.isEmpty ){
		tempStack.push( s.pop() );
		//look for tempStack item
		boolean found = false

		while( !found && !q.isEmpty() ){
			found = q.front().equals( tempStack.top() );
			//not matched put back, otherwise throw away so can't use again
			if( !found )
				tempQueue.enqueue( q.dequeue() );
		}

		result = found;
		//restore original queue
		while( !q.isEmpty() )
			tempQueue.enqueue( q.dequeue() );
		while(! tempQueue.isEmpty() )
			q.enqueue( tempQueue() );
	}
	//restore stack
	while( !tempStack.isEmpty() )
		s.push(temStack.pop() );
	return result;
}