算法第四版 练习1.3.33

Deque.java

import java.util.Iterator;public class Deque<Item> implements Iterable<Item>{    private class DoubleNode<Item>    {        private DoubleNode<Item> next = null;        private DoubleNode<Item> last = null;        private Item data;    }    private DoubleNode<Item> head = null;    public Deque()    {    }    public boolean isEmpty()    {        return head == null;    }    public int size()    {        if (head == null)            return 0;        DoubleNode<Item> current = head;        int count = 1;        while(current.next != null)        {            ++count;            current = current.next;        }        return count;    }    public void pushLeft(Item item)    {        if (head == null)        {            head = new DoubleNode<Item>();            head.data = item;            return;        }        DoubleNode<Item> current = new DoubleNode<Item>();        current.data = item;        current.next = head;        head.last = current;        head = current;    }    public void pushRight(Item item)    {        if (head == null)        {            head = new DoubleNode<Item>();            head.data = item;            return;        }        DoubleNode<Item> current = head;        while (current.next != null)            current = current.next;        current.next = new DoubleNode<Item>();        current.next.data = item;        current.next.last = current;    }    public Item popLeft()    {        if (head == null)            throw new RuntimeException();        Item ret = head.data;        head = head.next;        head.last = null;        return ret;    }    public Item popRight()    {        if (head == null)            throw new RuntimeException();        DoubleNode<Item> current = head;        while (current.next != null)            current = current.next;        Item ret = current.data;        current.last.next = null;        return ret;    }    public Iterator<Item> iterator()    {        return new DequeIterator();    }    private class DequeIterator implements Iterator<Item>    {        private DoubleNode<Item> current = head;        public boolean hasNext()        {            return current != null;        }        public void remove()        {        }        public Item next()        {            Item item = current.data;            current = current.next;            return item;        }    }}

ResizingArrayDeque.java

import java.util.Iterator;public class ResizingArrayDeque<Item> implements Iterable<Item>{    private Item[] item;    private int head;    private int tail;    @SuppressWarnings("unchecked")    public ResizingArrayDeque(int cap)    {        item = (Item[])(new Object[cap]);        if (cap <= 1)            throw new RuntimeException();        head = cap / 2;        tail = cap / 2;    }    public boolean isEmpty()    {        return head == tail;    }    public int size()    {        return tail - head;    }    public void resize(int size)    {        @SuppressWarnings("unchecked")        Item[] temp = (Item[])(new Object[size]);        int start = size / 2 - size() / 2;        int end = start + size();        for (int i = start,j = head; i < end; ++i,++j)                temp[i] = item[j];        item = temp;        head = start;        tail = end;    }    public void pushLeft(Item data)    {        if (head == 0)            resize(size() * 3);        item[--head] = data;    }    public void pushRight(Item data)    {        if (tail == item.length)            resize(3 * size());        item[tail++] = data;    }    public Item popLeft()    {        if(isEmpty())            return null;        Item ret = item[head];        item[head++] = null;        return ret;    }    public Item popRight()    {        if (isEmpty())            return null;        Item ret = item[--tail];        item[tail] = null;        return ret;    }    public Iterator<Item> iterator()    {        return new ResizingArrayDequeIterator();    }    public class ResizingArrayDequeIterator implements Iterator<Item>    {        private int current = head;        public boolean hasNext()        {            return current < tail;        }        public void remove()        {        }        public Item next()        {            Item ret = item[current++];            return ret;        }    }}

测试:main.java

import edu.princeton.cs.algs4.StdOut;public class Main {    public static void main(String[] args)    {         Deque<Integer> dq = new Deque<Integer>();         for (int i = 5 ; i >= 0; --i)             dq.pushLeft(i);         for (int i = 6; i <= 10; ++i)             dq.pushRight(i);         for (Integer it : dq)             StdOut.print(it + " ");         StdOut.println();         for (int i = 0; i < 5; ++i)         {             StdOut.print(dq.popRight() + " ");             StdOut.print(dq.popLeft() + " ");         }         StdOut.println();        ResizingArrayDeque<Integer> rd = new ResizingArrayDeque<Integer>(11);         for (int i = 5 ; i >= 0; --i)             rd.pushLeft(i);         for (int i = 6; i <= 10; ++i)             rd.pushRight(i);         for (Integer it : rd)             StdOut.print(it + " ");         StdOut.println();         for (int i = 0; i < 5; ++i)         {             StdOut.print(rd.popRight() + " ");             StdOut.print(rd.popLeft() + " ");         }    }}