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RandomizedQueue.java
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RandomizedQueue.java
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import java.util.Iterator;
import java.util.NoSuchElementException;
import edu.princeton.cs.algs4.StdRandom;
public class RandomizedQueue<Item> implements Iterable<Item> {
private Item[] rgArrays;
private int size;
public Iterator<Item> iterator(){
return new RandomIterator();
}
private class RandomIterator implements Iterator<Item> {
private int rank;
private Item[] iterArrays;
public RandomIterator(){
rank = size;
iterArrays = (Item[]) new Object[rank];
for(int i = 0; i < size; i++){
iterArrays[i] = rgArrays[i];
}
}
public boolean hasNext(){
return (rank > 0);
}
public Item next(){
if (rank == 0)
throw new NoSuchElementException("there are no more items");
int r = StdRandom.uniform(0, rank);
rank --;
Item item = iterArrays[r];
iterArrays[r] = iterArrays[rank];
iterArrays[rank] = item;
return item;
}
}
public RandomizedQueue(){
rgArrays = (Item[]) new Object[1];
size = 0;
}
private void validate(Item item){
if (item == null)
throw new IllegalArgumentException("the item is null");
}
public boolean isEmpty() {
return (size == 0);
}
public int size(){
return size;
}
private void resize(int cap) {
Item[] temp = (Item[]) new Object[cap];
for (int i = 0; i < size; i++)
temp[i] = rgArrays[i];
rgArrays = temp;
}
public void enqueue(Item item) {
validate(item);
rgArrays[size++] = item;
if (size == rgArrays.length)
resize(2 * rgArrays.length);
}
public Item dequeue() {
if (size == 0)
throw new NoSuchElementException("the RandomizeQueue is empty!");
int r = StdRandom.uniform(0, size);
size --;
Item delItem = rgArrays[r];
rgArrays[r] = rgArrays[size];
rgArrays[size] = null;
if (size> 0 && size == rgArrays.length / 4)
resize(rgArrays.length / 2 );
return delItem;
}
public Item sample(){
if (size == 0)
throw new NoSuchElementException("the RandomizeQueue is empty");
return rgArrays[StdRandom.uniform(0, size)];
}
}