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RandomizedQueue.java
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116 lines (99 loc) · 2.35 KB
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import edu.princeton.cs.algs4.StdRandom;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.Objects;
/**
* Created by merlin on 17/1/22.
*/
public class RandomizedQueue<Item> implements Iterable<Item> {
private Item[] s;
private int size;
private void resize(int capacity)
{
Item[] copy = (Item[]) new Object[capacity];
for (int i = 0; i < size; i++)
{
copy[i] = s[i];
}
s = copy;
}
public RandomizedQueue()
{
s = (Item[]) new Object[1];
size = 0;
}
public boolean isEmpty()
{
return size == 0;
}
public int size()
{
return size;
}
public Item sample()
{
if (size == 0)
throw new NoSuchElementException();
else
{
int i = StdRandom.uniform(size);
return s[i];
}
}
public void enqueue(Item item)
{
if (item == null)
throw new NullPointerException();
if (size == s.length)
resize(s.length * 2);
s[size++] = item;
}
public Item dequeue()
{
if (size == 0)
throw new NoSuchElementException();
int index = StdRandom.uniform(size);
Item item = s[index];
s[index] = s[--size];
s[size] = null;
if (size > 0 && size == s.length/4)
resize(s.length/2);
return item;
}
public Iterator<Item> iterator()
{
return new ArrayIterator();
}
public static void main(String[] args){
}
private class ArrayIterator implements Iterator<Item>
{
private Item[] items;
private Item current;
private int index;
public ArrayIterator()
{
index = 0;
items = (Item[]) new Object[size];
for(int i=0; i<size; i++)
items[i] = s[i];
StdRandom.shuffle(items);
}
public boolean hasNext()
{
return index < size;
}
public void remove()
{
throw new UnsupportedOperationException();
}
public Item next()
{
if(!hasNext())
throw new NoSuchElementException();
Item item = items[index];
index++;
return item;
}
}
}