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; } };
