第11天 Stack Queue

1.Stack

package algs4;

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

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

    private Node<Item> first;
    private int n;
    
    private static class Node<Item> {
        private Item item;
        private Node<Item> next;
    }
    
    public Stack() {
        first = null;
        n = 0;
    }
    
    public boolean isEmpty() {
        return first == null;
    }
    
    public int size() {
        return n;
    }
    
    public void push(Item item) {
        Node<Item> oldfirst = first;
        first = new Node<Item>();
        first.item = item;
        first.next = oldfirst;
        n++;
    }
    
    public Item pop() {
        if (isEmpty()) throw new NoSuchElementException("Stack underflow");
        Item item = first.item;
        first = first.next;
        n--;
        return item;
    
    }
    
    public Item peek() {
        if (isEmpty()) throw new NoSuchElementException("Stack underflow");
        return first.item;
    }
    
    public String toString() {
        StringBuilder s = new StringBuilder();
        for (Item item : this)
            s.append(item + " ");
        return s.toString();
    }
    
    @Override
    public Iterator<Item> iterator() {
        // TODO Auto-generated method stub
        return new ListIterator<Item>(first);
    }

    private class ListIterator<Item> implements Iterator<Item> {
        private Node<Item> current;
        
        public ListIterator(Node<Item> first) {
            // TODO Auto-generated constructor stub
            current = first;
        }

        @Override
        public boolean hasNext() {
            // TODO Auto-generated method stub
            return current != null;
        }

        @Override
        public Item next() {
            // TODO Auto-generated method stub
            if (!hasNext()) throw new NoSuchElementException();
            Item item = current.item;
            current = current.next;
            return item;
        }

        @Override
        public void remove() {
            // TODO Auto-generated method stub
            throw new UnsupportedOperationException();
        }
        
    }
    
    public static void main(String[] args) {
        Stack<String> stack = new Stack<String>();
//        while (!StdIn.isEmpty()) {
//            
//        }
    }
    
}

2.Queue

package algs4;

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






public class Queue<Item> implements Iterable<Item> {
    private Node<Item> first;
    private Node<Item> last;
    private int n;
    
    
    private static class Node<Item> {
        private Item item;
        private Node<Item> next;
    }
    
    public Queue() {
        first = null;
        last = null;
        n = 0;
    }
    
    public boolean isEmpty() {
        return first == null;
    }
    
    public int size() {
        return n;
    }
    
    public Item peek() {
        if (isEmpty()) throw new NoSuchElementException("Stack underflow");
        return first.item;
    }
    
    public void enqueue(Item item) {
        Node<Item> oldlast = last;
        last = new Node<Item>();
        last.item = item;
        last.next = null;
        if (isEmpty()) first = last;
        else oldlast.next = last;
        n++;
    }
    
    public Item dequeue() {
        if (isEmpty()) throw new NoSuchElementException("Stack underflow");
        Item item = first.item;
        first = first.next;
        n--;
        if (isEmpty()) last = null;
        return item;
    }
    
    

    public String toString() {
        StringBuilder s = new StringBuilder();
        for (Item item : this)
            s.append(item + " ");
        return s.toString();
    }
    
    @Override
    public Iterator<Item> iterator() {
        // TODO Auto-generated method stub
        return new ListIterator<Item>(first);
    }

    private class ListIterator<Item> implements Iterator<Item> {
        private Node<Item> current;
        
        public ListIterator(Node<Item> first) {
            // TODO Auto-generated constructor stub
            current = first;
        }

        @Override
        public boolean hasNext() {
            // TODO Auto-generated method stub
            return current != null;
        }

        @Override
        public Item next() {
            // TODO Auto-generated method stub
            if (!hasNext()) throw new NoSuchElementException();
            Item item = current.item;
            current = current.next;
            return item;
        }

        @Override
        public void remove() {
            // TODO Auto-generated method stub
            throw new UnsupportedOperationException();
        }
        
    }
}