Coursera Programming Assignment 2: Deques and Randomized Queues

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完整代码如下

Deque.java

import java.util.Iterator;
import java.util.NoSuchElementException;


public class Deque<Item> implements Iterable<Item> {

	private Node first, last;
	private int N;
	
	private class Node {
		Item value;
		Node next;
		Node pre;
		Node(Item item) {
			this.value = item;
			next = null;
			pre = null;
		}
	}
	
	public Deque() {
		N = 0;
		first = last = null;
	}

	public boolean isEmpty() {
		return N == 0;
	}

	public int size() {
		return N;
	}
	
	public void addFirst(Item item) {
		if(null == item) {
			throw new IllegalArgumentException();
		}
		Node node = new Node(item);
		
		
		if(isEmpty()) {
			first = last = node;
			N++;
			return;
		}
		N++;
		node.pre = null;
		node.next = first;
		
		first.pre = node;
		first = node;
		
	}

	public void addLast(Item item) {
		if(null == item) {
			throw new IllegalArgumentException();
		}
		Node node = new Node(item);
		
		if(isEmpty()) {
			first = last = node;
			N++;
			return;
		}
		
		N++;
		node.pre = last;
		node.next = null;
		last.next = node;
		last = node;
		
	}

	public Item removeFirst()   {
		if(isEmpty()) {
			throw new NoSuchElementException();
		}
		
		if(last == first) {
			Item ans = first.value;
			first = last = null;
			N = 0;
			return ans;
		}
		
		Node ans = first;
		Node second = first.next;
		
		second.pre = null;
		ans.next = null;
		
		first = second;
		N--;
		return ans.value;
	}

	public Item removeLast()      {
		if(isEmpty()) {
			throw new NoSuchElementException();
		}
		
		if(last == first) {
			Item ans = last.value;
			last = first = null;
			N = 0;
			return ans;
		}
		Node ans = last;
		Node pre = last.pre;
		
		ans.pre = null;
		pre.next = null;
		
		last = pre;
		N--;
		
		return ans.value;
	}
	

	
	private class MyIter implements Iterator<Item> {

		private Node current = null;
		
		public MyIter(Node first) {
			this.current = first;
		}
		
		@Override
		public boolean hasNext() {
			return current != null;
		}

		@Override
		public Item next() {
			if(!hasNext()) {
				throw new NoSuchElementException();
			}
			Item ans = current.value;
			current = current.next;
			return ans;
		}
		
		@Override
		public void remove() {
			throw new UnsupportedOperationException();
		}
		
	}

	
	@Override
	public Iterator<Item> iterator() {
		return new MyIter(first);
	}

}

RandomizedQueue.java

import java.util.Iterator;
import java.util.NoSuchElementException;

import com.sun.org.apache.bcel.internal.generic.NEW;

import edu.princeton.cs.algs4.StdRandom;

public class RandomizedQueue<Item> implements Iterable<Item> {

	private Item[] queue;
	private int size = 0; // the number of current element in the queue
	
	
	public RandomizedQueue() {
		queue = (Item[]) new Object[8];
		size = 0;
	}

	public boolean isEmpty() {
		return size == 0;
	}

	public int size() {
		return size;
	}

	public void enqueue(Item item) {
		if(null == item) {
			throw new IllegalArgumentException();
		}
		if(size == queue.length) {
			resize(2 * queue.length);
		}
		queue[size++] = item;
	}
	
	
	private void resize(int newLen) {
		Item[] temp = (Item[]) new Object[newLen];
		for(int i = 0; i < size; i++) {
			temp[i] = queue[i];
		}
		queue = temp;
	}
	
	public Item dequeue() {
		if(isEmpty()) {
			throw new NoSuchElementException();
		}
		int index = StdRandom.uniform(size);
		Item item = queue[index];
		// Delete an element, and move the last element to the deleted index
		if(index != size - 1) {
			queue[index] = queue[size - 1];
		}
		queue[size - 1] = null;
		size--;
		if(size > 0 && size == queue.length / 4) {
			resize(queue.length / 2);
		}
		return item;
	}

	public Item sample() {
		if(isEmpty()) {
			throw new NoSuchElementException();
		}
		return queue[StdRandom.uniform(size)];
	}

	private class MyIter implements Iterator<Item> {

		private Item[] items = (Item[])new Object[queue.length];
		private int n = size;
		
		public MyIter() {
			for(int i = 0; i < queue.length; i++) {
				items[i] = queue[i];
			}
		}
		
		@Override
		public boolean hasNext() {
			return n != 0;
		}

		@Override
		public Item next() {
			if(!hasNext()) {
				throw new NoSuchElementException();
			}
			int index = StdRandom.uniform(n);
			Item item = items[index];
			if(index != n - 1) {
				items[index] = items[n - 1];
			}
			items[n - 1] = null;
			n--;
			return item;
		}
		
		@Override
		public void remove() {
			throw new UnsupportedOperationException();
		}
		
	}
	
	public Iterator<Item> iterator() {
		return new MyIter();
	}
}

Permutation.java

import edu.princeton.cs.algs4.StdIn;

public class Permutation {

	public static void main(String[] args) {
		int k = Integer.valueOf(args[0]);
		String str = null;
		RandomizedQueue<String> queue = new RandomizedQueue<String>();
		while(!StdIn.isEmpty()) {
			str = StdIn.readString();
			queue.enqueue(str);
		}
		
		
		
		for(int i = 0; i < k; i++) {
			String string = queue.dequeue();
			System.out.println(string);
		}
	}
}