LeetCode: Valid Parentheses

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.

   bool isValid(string s) {  
     stack<char> S;  
     int n = s.length();  
   
     for(int i = 0; i < n; i++)  
     {  
       if(s[i] == '(' || s[i] == '{' || s[i] == '[')S.push(s[i]);  
       else if (s[i] == ')' || s[i] == '}' || s[i] == ']')  
       {  
         if(S.empty())return false;  
         char t = S.top();  
         S.pop();  
         if((s[i] == ')' && t!= '(') ||  
           (s[i] == '}' && t!= '{') ||  
           (s[i] == ']' && t!= '[') )return false;  
       }  
     }  
     if(!S.empty())return false;  
     return true;  
   }