用链表实现背包，队列，栈

栈

package com.ttpfx.fundamentals.linked;

import edu.princeton.cs.algs4.StdIn;
import edu.princeton.cs.algs4.StdOut;

public class LinkedStack<Item> {
    private Node first = null;
    private int size;

    private class Node {
        Item item;
        Node next;
    }

    public boolean isEmpty() {
        return first == null;
    }

    public int size() {
        return size;
    }

    public void push(Item item) {
        Node oldFirst = first;

        first = new Node();
        first.item = item;
        first.next = oldFirst;

        size++;
    }

    public Item pop() {
        Item item = first.item;
        first = first.next;
        size--;
        return item;
    }

    // 测试输入：to be or not to - be - - that - - - is
    public static void main(String[] args) {
        LinkedStack<String> stack = new LinkedStack<>();
        while (!StdIn.isEmpty()) {
            String item = StdIn.readString();
            if (!item.equals("-")) {
                stack.push(item);
            } else if (!stack.isEmpty()) {
                StdOut.print(stack.pop() + " ");
            }
        }
        StdOut.println("(" + stack.size() + " left on stack)");
    }
}

队列

package com.ttpfx.fundamentals.linked;

import edu.princeton.cs.algs4.StdIn;
import edu.princeton.cs.algs4.StdOut;

public class LinkedQueue<Item> {
    private Node first;
    private Node last;
    private int size;

    private class Node {
        Item item;
        Node next;
    }

    /**
     * 添加一个元素
     */
    public void enqueue(Item item) {
        Node oldLast = last;

        last = new Node();
        last.item = item;

        if (oldLast == null) {
            first = last;
        } else {
            oldLast.next = last;
        }

        size++;
    }

    /**
     * 删除最早添加的元素
     */
    public Item dequeue() {
        if (isEmpty()) {
            return null;
        }

        Item item = first.item;
        if (first == last) {
            first = null;
            last = null;
        } else {
            first = first.next;
        }

        size--;

        return item;
    }

    public boolean isEmpty() {
        return first == null;
    }

    public int size() {
        return size;
    }

    // 测试：to be or not to - be - - that - - - is
    public static void main(String[] args) {
        LinkedQueue<String> queue = new LinkedQueue<String>();
        while (!StdIn.isEmpty()) {
            String item = StdIn.readString();
            if (!item.equals("-")) {
                queue.enqueue(item);
            } else if (!queue.isEmpty()) {
                StdOut.print(queue.dequeue() + " ");
            }
        }
        StdOut.println("(" + queue.size() + " left on queue)");
    }
}

背包

package com.ttpfx.fundamentals.linked;

import edu.princeton.cs.algs4.StdIn;
import edu.princeton.cs.algs4.StdOut;

import java.util.Iterator;

public class LinkedBag<Item> implements Iterable<Item> {
    private Node first = null;
    private int size;

    private class Node {
        Item item;
        Node next;
    }

    public boolean isEmpty() {
        return first == null;
    }

    public int size() {
        return size;
    }

    public void add(Item item) {
        Node oldFirst = first;

        first = new Node();
        first.item = item;
        first.next = oldFirst;

        size++;
    }

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

    private class ListIterator implements Iterator<Item> {
        private Node node = first;

        @Override
        public boolean hasNext() {
            return node != null;
        }

        @Override
        public Item next() {
            Item item = node.item;
            node = node.next;
            return item;
        }
    }

    // 测试输入：to be or not to be that is a question
    public static void main(String[] args) {
        LinkedBag<String> bag = new LinkedBag<>();

        while (!StdIn.isEmpty()) {
            String item = StdIn.readString();
            bag.add(item);
        }

        for (String s : bag) {
            StdOut.println(s);
        }
    }
}