package QuestionEight;class EmptyStackException extends Exception { EmptyStackException(String s) { super(s); }}class UnknownStackException extends Exception { UnknownStackException(String s) { super(s); }}/** * Create a two-sided stack. One stack starts at 0, the other at length - 1, * and as they grow they approach eachother. Given the constraints of the * question, the FullStackException class was not required. * @author Peter Goodman */class RedBlueStack<E> { protected int[] height = {0, 0}; protected int[] start = {0, 0}; protected E[] stack; /* How we will address each stack, enum was overly complex. */ static public final int RED = 0; static public final int BLUE = 0; /** Constructor, set the pertinent info so we can work with 2 stacks. */ public RedBlueStack(int N) { stack = (E[]) new Object[N]; start[BLUE] = N - 1; } /** Get the size of a given stack */ public int size(int s) throws UnknownStackException { if(s < 0 || s > 1) throw new UnknownStackException("Stack doesn't exist."); return height[s]; } /** Is one of the stacks empty? */ public boolean isEmpty(int s) throws UnknownStackException { return (size(s) == 0); } /** Push an element onto one of the stacks */ public void push(int s, E elem) throws UnknownStackException { int index = Math.abs(start[s] - height[s]); stack[index] = elem; height[s]++; } /** Pop an element off of one of the stacks */ public E pop(int s) throws EmptyStackException, UnknownStackException { if(isEmpty(s)) throw new EmptyStackException("Stack is empty."); int index = Math.abs(start[s] - height[s]) - 1; E elem = stack[index]; stack[index] = null; return elem; } /** Get the top element from one of the stacks. */ public E top(int s) throws EmptyStackException, UnknownStackException { if(isEmpty(s)) throw new EmptyStackException("Stack is empty."); return stack[Math.abs(start[s] - height[s]) - 1]; } /* Stupid convenience functions */ public void pushRed(E elem) throws UnknownStackException { push(RED, elem); } public void pushBlue(E elem) throws UnknownStackException { push(BLUE, elem); } public E popRed() throws EmptyStackException, UnknownStackException { return pop(RED); } public E popBlue() throws EmptyStackException, UnknownStackException { return pop(BLUE); } public E topRed() throws EmptyStackException, UnknownStackException { return top(RED); } public E topBlue() throws EmptyStackException, UnknownStackException { return top(BLUE); } public int sizeRed() throws UnknownStackException { return size(RED); } public int sizeBlue() throws UnknownStackException { return size(BLUE); } public boolean isEmptyRed() throws UnknownStackException { return isEmpty(RED); } public boolean isEmptyBlue() throws UnknownStackException { return isEmpty(BLUE); }}