栈的实现

Java版本

1.使用链表的方式来实现栈

          这个Stack的实现版本使用了Java里面的泛型、迭代器的功能。例如，Stack实现了Iterable接口，这使得Stack能够支持Java中的for-each功能。

public interface Iterable<E>
{
	Iterator<E> iterator();
}

          可以这样使用Stack:

Stack<String> stack = new Stack<>();           // 使用Java7 的菱形运算符
stack.push( "Java" );
stack.push( "C++" );
stack.push( "C" );
for( String elem : stack )
        System.out.println( elem );

          Stack的完整实现：

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

public class Stack<T> implements Iterable<T>
{
	private int count;
	private Node<T> first;

	private static class Node<T>
	{
		private T elem;
		private Node<T> next;
	}    

	public void push( T elem )
	{
		Node<T> temp = new Node<>();         // 使用Java7 的菱形运算符
		temp.elem = elem;
		temp.next = first;
		first = temp;
		count++;
	}
	public String toString()
	{
		StringBuilder s = new StringBuilder();
		s.append( "[ " );
		for( T elem : this )
			s.append( elem + " " );
		s.append( "]" );
		return s.toString();
	}
	public T peek()
	{
		if( isEmpty() )
			throw new NoSuchElementException( "Stack underflow" );
		return first.elem;
	}

	public T pop()
	{
		if( isEmpty() )
			throw new NoSuchElementException( "Stack underflow" );
		T elem = first.elem;
		first = first.next;
		count--;
		return elem;
	}

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

	public int size()
	{
		return count;
	}

	private class ListIterator implements Iterator<T>
	{
		private Node<T> current = first;
		@Override
		public boolean hasNext()
		{
			return current != null;
		}
		@Override 
		public T next()
		{
			if( !hasNext() )
				throw new NoSuchElementException();
			T elem = current.elem;
			current = current.next;
			return elem;
		}
		@Override
		public void remove()
		{
			throw new UnsupportedOperationException();
		}
	}

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

使用动态数组来实现

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

public class ResizingArrayStack<T> implements Iterable<T>
{
	private T[] data;
	private int count;

	@SuppressWarnings("unchecked")
	public ResizingArrayStack()
	{
		data = ( T[] )new Object[2];
	}
	public boolean isEmpty()
	{
		return count == 0;
	}

	public void push( T elem )
	{
		if( count >= data.length )
			resize( data.length * 2 );
		data[count++] = elem;
	}

	@SuppressWarnings("unchecked")
	public void resize( int newSize )
	{
		T[] newData = ( T[] )new Object[newSize];
		for( int i = 0; i < count; i++ )
			newData[i] = data[i];
		data = newData;
	}

	public T pop()
	{
		if( isEmpty() )
			throw new NoSuchElementException( "Stack underflow" );
		T elem = data[count - 1];
		data[count - 1] = null;
		count--;
		if( count > 0 && count == data.length / 4 )
			resize( data.length / 2 );
		return elem;
	}
	public T peek()
	{
		if( isEmpty() )
			throw new NoSuchElementException( "Stack underflow" );
		return data[count - 1];
	}

	public int size()
	{
		return count;
	}
	public Iterator<T> iterator()
	{
		return new ReverseArrayIterator();
	}
	private class ReverseArrayIterator implements Iterator<T>
	{
		private int c = count;

		@Override
		public boolean hasNext()
		{
			return c > 0;
		}
		@Override
		public T next()
		{
			if( !hasNext() )
				throw new NoSuchElementException();
			return data[--c];
		}
		@Override
		public void remove()
		{
			throw new UnsupportedOperationException();
		}
	}
}

2、C++版本

待续...