20 Valid Parentheses(匹配括号)

class Solution {
public:
    bool isValid(string s) {
        if(s==""||s.size()%2==1)
            return false;
        stack<char> mystack;
        for(int i=0;i<s.length();++i){
            if(s[i]==‘[‘||s[i]==‘(‘||s[i]==‘{‘){
                mystack.push(s[i]);
                continue;
            }
            else{
                if(s[i]){
                    if(mystack.empty())
                    return false;
                }
                switch(s[i]){
                    case ‘]‘:
                        if(mystack.top()!=‘[‘)
                            return false;
                        else
                            mystack.pop();
                        break;
                    case ‘)‘:
                        if(mystack.top()!=‘(‘)
                            return false;
                        else mystack.pop();
                        break;
                    case ‘}‘:
                        if(mystack.top()!=‘{‘)
                            return false;
                        else mystack.pop();
                        break;
                }
            }
        }
        if(mystack.empty())
            return true;
        return false;
    }
};