本人正在学数据结构的链表，请教一下如何用链表来进行括号匹配，能否举个代码例子。还有一个练习就是如何用链表先通过前序方式建立二叉树，再通过层次遍历二叉树，求代码。谢了！！

关于括号匹配，我已经用堆栈写出来了，不过还是有点小错误，我把代码发上，大家帮忙看一下。还有第二个练习题，也可以有堆栈做，我暂时还没写出来，希望高手发个代码上来，帮我参考参考。。。
import java.util.*;
class Node
{
    Object data;
    Node next;
    public Node(Object obj,Node next)
    {
        data=obj;
        this.next=next;
    }
}
class LinStack
{
    Node head;
    int size;
    public void LinStack()
    {
        head=null;
        size=0;
    }
    public void push(Object obj)
    {
        head=new Node(obj,head);
        size++;
    }
    public Object pop() throws Exception
    {
        Object obj=head.data;
        head=head.next;
        size--;
        return obj;
    }
    public boolean notEmpty()
    {
        return head != null;
    }
    public Object getTop()
    {
        return head.data;
    }
}
public class StackTest
{
    public static void main(String args[])throws Exception
    {
        String str;
        LinStack stack=new LinStack();
        Scanner reader =new Scanner(System.in);
        System.out.println("请输入括号：");
        str=reader.nextLine();
        char ch;
        for(int i=0;i<str.length();i++)
        {
            ch=str.charAt(i);
            if(ch=='('||ch=='['||ch=='{')
                stack.push(ch);
            else if(ch==')'&& stack.notEmpty()&& stack.getTop().equals('('))
                stack.pop();
            else if(ch==')'&& stack.notEmpty()&& ! stack.getTop().equals('('))
            {
                System.out.println("左右括号不匹配");
                return;
            }        
            else if(ch==']'&& stack.notEmpty()&& stack.getTop().equals('['))
                stack.pop();
            else if(ch==']'&& stack.notEmpty()&& ! stack.getTop().equals('['))
            {
                System.out.println("左右括号不匹配");
                return;
            }
            else if(ch=='}'&& stack.notEmpty()&& stack.getTop().equals('{'))
                stack.pop();
            else if(ch=='}'&& stack.notEmpty()&& ! stack.getTop().equals('{'))
            {
                System.out.println("左右括号不匹配");
                return;
            }
            else if(ch==')'||ch==']'||ch=='}'&& ! stack.notEmpty())
            {
                System.out.println("右括号多于左括号！");
                return;
            }                    
        }
        if(stack.notEmpty())
            System.out.println("左括号多于右括号！");
        else
            System.out.println("左右括号匹配");
    }
}