算法（Algorithms）第4版 练习 1.3.7

package com.qiusongde;

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

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

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

private Node first;
private int n;

private class Node {
Item item;
Node next;
}

public Stack() {
first = null;
n = 0;
}

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

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

n++;
}

public Item pop() {

if(isEmpty())
throw new NoSuchElementException("Stack is empty");

Item item = first.item;
first = first.next;
n--;

return item;
}

//1.3.7
public Item peek() {
if(isEmpty())
throw new NoSuchElementException("Stack is empty");

return first.item;
}

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

public int size() {
return n;
}

@Override
public Iterator<Item> iterator() {

return new StackIterator();
}

private class StackIterator implements Iterator<Item> {

private Node current = first;

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

@Override
public Item next() {
if(!hasNext())
throw new NoSuchElementException("Stack is empty");

Item item = current.item;
current = current.next;

return item;
}

@Override
public void remove() {
throw new UnsupportedOperationException("Stack don't support remove");
}

}

public static void main(String[] args) {

Stack<String> stack = new Stack<String>();
StdOut.println("Initialized size:" + stack.size());

while (!StdIn.isEmpty()) {

String item = StdIn.readString();

if (!item.equals("-")) {

stack.push(item);
StdOut.println("push success:" + item + " size:" + stack.size());

StdOut.print("Left on stack: ");
for (String s : stack) {
StdOut.print(s + " ");
}
StdOut.println();

} else {
if(stack.isEmpty())
StdOut.println("pop error, stack empty");
else {
StdOut.println("pop success:" + stack.pop() + " size:" + stack.size());

StdOut.print("Left on stack: ");
for (String s : stack) {
StdOut.print(s + " ");
}
StdOut.println();
}
}

}

}

}