Valid Parentheses

1、Valid Parentheses 括号的匹配
题目：
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.
思路：
1、设计一个堆栈stack，将’(‘, ‘{‘, ‘[‘放进去；
2、如果为 ‘)’, ‘{‘, ‘}’, ‘[’ and ‘]’，则判断堆栈顶端是否为相对应的括号形式，如果不对应，则为false；
3、如果最后堆栈为空，则表示全都匹配过了，返回为真；
代码：

class Solution {
public:
    bool isValid(string s) {
        stack<char> charstack;
        for(int i=0;i<s.length();i++)
        {
            char charParenthes=s[i];
            if(charParenthes!=')' && charParenthes!='}' && charParenthes!=']') 
             charstack.push(charParenthes);

            else
            {
                if(charstack.size()==0) return false;
                char top=charstack.top();
                switch(charParenthes)
                {
                    case ')':
                        if(top=='(') charstack.pop();
                        else
                           return false;
                        break;

                    case '}':
                        if(top=='{') charstack.pop();
                        else
                            return false;
                        break;

                    case ']':
                        if(top=='[') charstack.pop();
                        else
                            return false;
                        break;

                }
            }
        }
        if(charstack.size()==0) return true;
        else  return false;
    }
};