There's a syntax error in this code, and I'm not sure how to get it to run. This is code from a Chegg Textbook Solution, "Algorithms (4th Edition)" Chapter 2.2 Problem 14E and 15E.
The following lines (lines 10 and 11 of the first class) are causing the error:
Queue> ques = new
LinkedList>();
All quick suggestions have been exhausted.
Bottom Up Merge Sort (Class with error)
package Exercise2;
import java.util.Queue; //for add etc m...cedure
import java.util.LinkedList;
public class BottomUpMergeSort{
public static Queue sort(Double[] a)
{
int N = a.length;
// Create a queue of the N queues,
Queue> ques = new
LinkedList>();//These two lines have an error
for (int i = 0; i < N; i++)
{
// Each of the N queues contains a single
// item
Queue m = new LinkedList();
m.add(a[i]);
// add this single item queue to parent
// queue
ques.add(m);
}
// Repeat till queue of the N queues contains
// a single queue.
while (ques.size() > 1)
{
// apply the merging operation from 2.2.14
Queue que1 = ques.remove();
Queue que2 = ques.remove();
Queue r = E2_2_14.merge(que1, que2);
// insert the merged queue at the end of
// parent queues.
ques.add(r);
}
// remove and return the single sorted queue
//left return
}
// print the array elements
public static void printArr(Double[] a)
{
for (int i = 0; i < a.length; i++) {
System.out.print(a[i] + "\t ");
System.out.println();
}
}
}
MERGE SORTED CLASS
package Exercise2;
public class MergeSortedQueues{
public static void main(String[] args) {
Queue<Double> Q1 = new Queue<Double>();
Queue<Double> Q2 = new Queue<Double>();
Q1.enqueue(2.0);
Q1.enqueue(4.0);
Q1.enqueue(6.0);
Q1.enqueue(8.0);
Q2.enqueue(1.0);
Q2.enqueue(3.0);
Q2.enqueue(5.0);
Q2.enqueue(7.0);
//printQueue(Q1);
//printQueue(Q2);
Queue que=merge(Q1, Q2);
printQueue(que);
}
public static Queue merge(Queue Q1, Queue Q2) {
if(Q1.isEmpty()) return Q2;
if (Q2.isEmpty())return Q1;
Queue Q3=new Queue();
int len1=Q1.size();
int len2=Q2.size();
int i=0, j=0;
Comparable x,y;
while(i<len1||j<len2) {
if(i<len1&&j<len2) {
x=(Comparable) Q1.peek();
y=(Comparable) Q2.peek();
if(less(x,y)) {
Q1.dequeue();
Q3.enqueue(x);
Q1.enqueue(x);
i++;
}
else {
Q2.dequeue();
Q3.enqueue(y);
Q2.enqueue(y);
j++;
}
}
else if(i<len1&&j>=len2) {
x=(Comparable)Q1.dequeue();
Q1.enqueue(x);
Q3.enqueue(x);
i++;
}
else if (i>len1&&j<len2)
{
y=(Comparable) Q1.dequeue();
Q2.enqueue(y);
Q3.enqueue(y);
j++;
}
}
return Q3;
}
private static boolean less(Comparable x, Comparable y) {
return x.compareTo(y)<0;
}
public static void printQueue(Queue que) {
for(Object item:que) {
System.out.println(item);
}
}
}
QUEUE INTERFACE
package Exercise2;
import java.util.Iterator;
import java.util.NoSuchElementException;
public class Queue<Item> implements Iterable<Item> {
private Node<Item> first; // beginning of queue
private Node<Item> last; // end of queue
private int n; // number of elements on queue
// helper linked list class
private static class Node<Item> {
private Item item;
private Node<Item> next;
}
/**
* Initializes an empty queue.
*/
public Queue() {
first = null;
last = null;
n = 0;
}
/**
* Returns true if this queue is empty.
*
* @return {@code true} if this queue is empty; {@code false} otherwise
*/
public boolean isEmpty() {
return first == null;
}
/**
* Returns the number of items in this queue.
*
* @return the number of items in this queue
*/
public int size() {
return n;
}
/**
* Returns the item least recently added to this queue.
*
* @return the item least recently added to this queue
* @throws NoSuchElementException if this queue is empty
*/
public Item peek() {
if (isEmpty()) throw new NoSuchElementException("Queue underflow");
return first.item;
}
/**
* Adds the item to this queue.
*
* @param item the item to add
*/
public void enqueue(Item item) {
Node<Item> oldlast = last;
last = new Node<Item>();
last.item = item;
last.next = null;
if (isEmpty()) first = last;
else oldlast.next = last;
n++;
}
public Item dequeue() {
if (isEmpty()) throw new NoSuchElementException("Queue underflow");
Item item = first.item;
first = first.next;
n--;
if (isEmpty()) last = null; // to avoid loitering
return item;
}
/**
* Returns a string representation of this queue.
*
* @return the sequence of items in FIFO order, separated by spaces
*/
public String toString() {
StringBuilder s = new StringBuilder();
for (Item item : this) {
s.append(item);
s.append(' ');
}
return s.toString();
}
/**
* Returns an iterator that iterates over the items in this queue in
FIFO order.
*
* @return an iterator that iterates over the items in this queue in
FIFO order
*/
public Iterator<Item> iterator() {
return new ListIterator<Item>(first);
}
// an iterator, doesn't implement remove() since it's optional
private class ListIterator<Item> implements Iterator<Item> {
private Node<Item> current;
public ListIterator(Node<Item> first) {
current = first;
}
public boolean hasNext() { return current != null; }
public void remove() { throw new UnsupportedOperationException(); }
public Item next() {
if (!hasNext()) throw new NoSuchElementException();
Item item = current.item;
current = current.next;
return item;
}
}
}
There's a syntax error that I can't work around.
答案 0 :(得分：1)
The problem is in the following line(s):
Queue> ques = new LinkedList>();
The two >s in that line are causing the problem.
If you don't want to specify exactly which type of object is in the queue, do this:
Queue ques = new LinkedList();
Preferably, if you want to specific which type of object can be stored in the queue, do this:
Queue<Queue> ques = new LinkedList<Queue>();
... which can be shortened to:
Queue<Queue> ques = new LinkedList<>();