MUST USE THIS QUEUE CLASS: */ package algs13; import stdlib.*; import java.util.
ID: 3746066 • Letter: M
Question
MUST USE THIS QUEUE CLASS:
*/
package algs13;
import stdlib.*;
import java.util.Iterator;
import java.util.NoSuchElementException;
/* ***********************************************************************
* Compilation: javac Queue.java
* Execution: java Queue < input.txt
* Data files: http://algs4.cs.princeton.edu/13stacks/tobe.txt
*
* A generic queue, implemented using a linked list.
*
* % java Queue < tobe.txt
* to be or not to be (2 left on queue)
*
*************************************************************************/
/**
* The <tt>Queue</tt> class represents a first-in-first-out (FIFO)
* queue of generic items.
* It supports the usual <em>enqueue</em> and <em>dequeue</em>
* operations, along with methods for peeking at the top item,
* testing if the queue is empty, and iterating through
* the items in FIFO order.
* <p>
* All queue operations except iteration are constant time.
* <p>
* For additional documentation, see <a href="http://algs4.cs.princeton.edu/13stacks">Section 1.3</a> of
* <i>Algorithms, 4th Edition</i> by Robert Sedgewick and Kevin Wayne.
*/
public class Queue<T> implements Iterable<T> {
private int N; // number of elements on queue
private Node<T> first; // beginning of queue
private Node<T> last; // end of queue
// helper linked list class
private static class Node<T> {
public Node() { }
public T item;
public Node<T> next;
}
/**
* Create an empty queue.
*/
public Queue() {
first = null;
last = null;
N = 0;
}
/**
* Is the queue empty?
*/
public boolean isEmpty() {
return first == null;
}
/**
* Return the number of items in the queue.
*/
public int size() {
return N;
}
/**
* Return the item least recently added to the queue.
* @throws java.util.NoSuchElementException if queue is empty.
*/
public T peek() {
if (isEmpty()) throw new NoSuchElementException("Queue underflow");
return first.item;
}
/**
* Add the item to the queue.
*/
public void enqueue(T item) {
Node<T> oldlast = last;
last = new Node<>();
last.item = item;
last.next = null;
if (isEmpty()) first = last;
else oldlast.next = last;
N++;
}
/**
* Remove and return the item on the queue least recently added.
* @throws java.util.NoSuchElementException if queue is empty.
*/
public T dequeue() {
if (isEmpty()) throw new NoSuchElementException("Queue underflow");
T item = first.item;
first = first.next;
N--;
if (isEmpty()) last = null;
return item;
}
/**
* Return string representation.
*/
public String toString() {
StringBuilder s = new StringBuilder();
for (T item : this)
s.append(item + " ");
return s.toString();
}
// check internal invariants
private static <T> boolean check(Queue<T> that) {
int N = that.N;
Queue.Node<T> first = that.first;
Queue.Node<T> last = that.last;
if (N == 0) {
if (first != null) return false;
if (last != null) return false;
}
else if (N == 1) {
if (first == null || last == null) return false;
if (first != last) return false;
if (first.next != null) return false;
}
else {
if (first == last) return false;
if (first.next == null) return false;
if (last.next != null) return false;
// check internal consistency of instance variable N
int numberOfNodes = 0;
for (Queue.Node<T> x = first; x != null; x = x.next) {
numberOfNodes++;
}
if (numberOfNodes != N) return false;
// check internal consistency of instance variable last
Queue.Node<T> lastNode = first;
while (lastNode.next != null) {
lastNode = lastNode.next;
}
if (last != lastNode) return false;
}
return true;
}
/**
* Return an iterator that iterates over the items on the queue in FIFO order.
*/
public Iterator<T> iterator() {
return new ListIterator();
}
// an iterator, doesn't implement remove() since it's optional
private class ListIterator implements Iterator<T> {
private Node<T> current = first;
public boolean hasNext() { return current != null; }
public void remove() { throw new UnsupportedOperationException(); }
public T next() {
if (!hasNext()) throw new NoSuchElementException();
T item = current.item;
current = current.next;
return item;
}
}
public void toGraphviz(String filename) {
GraphvizBuilder gb = new GraphvizBuilder ();
toGraphviz (gb, null, first);
gb.toFile (filename, "rankdir="LR"");
}
private void toGraphviz (GraphvizBuilder gb, Node<T> prev, Node<T> n) {
if (n == null) { gb.addNullEdge (prev); return; }
gb.addLabeledNode (n, n.item.toString ());
if (prev != null) gb.addEdge (prev, n);
toGraphviz (gb, n, n.next);
}
/**
* A test client.
*/
public static void main(String[] args) {
StdIn.fromString ("to be or not to - be - - that - - - is");
Queue<String> q = new Queue<>();
int count = 0;
q.toGraphviz ("queue" + count + ".png"); count++;
while (!StdIn.isEmpty()) {
String item = StdIn.readString();
if (!item.equals("-")) q.enqueue(item);
else if (!q.isEmpty()) StdOut.print(q.dequeue() + " ");
q.toGraphviz ("queue" + count + ".png"); count++;
}
StdOut.println("(" + q.size() + " left on queue)");
}
}
*/
* mergeQueues
* precondition: input queues q1, q2 may be empty
* postconditions:
* return a new queue containing merged contents of q1,q2 using
* an every-other-one policy - starting with q1
* if queues are not the same length, the 'tail' of the longer one ends
* up getting appended to the result - see examples below
* original queues are empty
* you may use: basic java arrays, Stack<>, Queue<> from algs13
* you may NOT use any other Java classes, algorithms without permission
* your solution must be all client code: you may not alter the original Stack, Queue classes
* In the examples below, the left-most values are at the front of the queues
* Examples:
* q1: abcd , q2: wxyz mergeQueues(q1,q2) --> awbxcydz
* q1: abc , q2: xy mergeQueues(q1,q2) --> axbyc
* q1: ab , q2: xyz mergeQueues(q1,q2) --> axbyz
* q1: abc , q2: mergeQueues(q1,q2) --> abc
* q1: , q2: mergeQueues(q1,q2) -->
* merge
*/
public static Queue<String> mergeQueues(Queue<String> q1,Queue<String> q2) {
Explanation / Answer
here is your function : ------------------>>>>>>>>>>>
*/
* mergeQueues
* precondition: input queues q1, q2 may be empty
* postconditions:
* return a new queue containing merged contents of q1,q2 using
* an every-other-one policy - starting with q1
* if queues are not the same length, the 'tail' of the longer one ends
* up getting appended to the result - see examples below
* original queues are empty
* you may use: basic java arrays, Stack<>, Queue<> from algs13
* you may NOT use any other Java classes, algorithms without permission
* your solution must be all client code: you may not alter the original Stack, Queue classes
* In the examples below, the left-most values are at the front of the queues
* Examples:
* q1: abcd , q2: wxyz mergeQueues(q1,q2) --> awbxcydz
* q1: abc , q2: xy mergeQueues(q1,q2) --> axbyc
* q1: ab , q2: xyz mergeQueues(q1,q2) --> axbyz
* q1: abc , q2: mergeQueues(q1,q2) --> abc
* q1: , q2: mergeQueues(q1,q2) -->
* merge
*/
public static Queue<String> mergeQueues(Queue<String> q1,Queue<String> q2) {
Queue<String> result = new Queue<>();
while(!q1.isEmpty() && !q2.isEmpty()){
try{
result.enqueue(q1.dequeue());
result.enqueue(q2.dequeue());
}catch(Exception e){
}
}
while(!q1.isEmpty()){
try{
result.enqueue(q1.dequeue());
}catch(Exception e){
}
}
while(!q2.isEmpty()){
try{
result.enqueue(q2.dequeue());
}catch(Exception e){
}
}
return result;
}
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