ValidParenthesis.md

class Solution { public: bool isValid(string expression) { stack s; for(int i=0; i<expression.length(); i++) {

     char ch = expression[i];
     
     //if opening bracket, stack push
     //if close bracket, stacktop check and pop
     
     if(ch == '(' || ch == '{' || ch == '['){
         s.push(ch);
     }
     else
     {
         //for closing bracket
         if(!s.empty()) {
              char top = s.top();
              if( (ch == ')' && top == '(') || 
                 ( ch == '}' && top == '{') || 
                 (ch == ']' && top == '[') ) {
                  s.pop();
              }
             else
             {
                 return false;
             }
         }
         else
         {
             return false;
         } 
     }  
 }

if(s.empty())
    return true;
else
    return false;

} };