題目：Given a string containing just the characters'(',')','{','}','['and']', determine if the input string is valid.
The brackets must close in the correct order,"()"and"()[]{}"are all valid but"(]"and"([)]"are not.
解題思路：括號匹配問題是典型的棧的應用題，示例代碼如下：
public class Solution
{
public boolean isValid(String s)
{
Stack<character> temp=new Stack<character>();
boolean flag=true;
for(int i=0;i<s.length();i++) switch="" case="" :="" flag="false;" default:="" return="" else="" pre=""><p>
</p>
</s.length();i++)></character></character>
