class Solution {
public:
    bool isValid(string s) {
        string s1 = "";

        for(int i=0;i<s.length();i++)
        {
            switch(s1.back())
            {
                case '(': if ( (s[i]=='}') || (s[i]==']') )
                            return false;
                          if ( s[i]==')' )
                          {
                              s1.pop_back();
                              break;
                          }
                          s1.push_back(s[i]);
                          break;
                case '{': if ( (s[i]==')') || (s[i]==']') )
                            return false;
                          if ( s[i]=='}' )
                          {
                              s1.pop_back();
                              break;
                          }
                          s1.push_back(s[i]);
                          break;
                case '[': if ( (s[i]==')') || (s[i]=='}') )
                            return false;
                          if ( s[i]==']' )
                          {
                              s1.pop_back();
                              break;
                          }
                          s1.push_back(s[i]);
                          break;
                default: s1.push_back(s[i]);
            }


        }

        if (s1=="")
            return true;
        else return false;

    }
};