Transform the Expression - ONP

test1.cpp

#include <iostream>
#include <stack>

using namespace std;

string reversePolishNotation(string expression){
	stack<char> operatorStack;
	string result = "";
	for(int i=0; i<expression.length(); i++){
		//If it is '(' then ignore
		if(expression[i] == '('){
			continue;
		}
		//Keep writing operands to the result string
		else if(isalpha(expression[i])){
			result += expression[i];
		}
		//When you encounter a ')' pop the operator from the operator stack
		else if(expression[i] == ')'){
			result += operatorStack.top();
			operatorStack.pop();
		}
		//When you encounter a operator, push it to the operator stack
		else{
			operatorStack.push(expression[i]);
		}
	}
	return result;
}

int main(){
	//For Fast IO
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);

	int t;
	string expression;
	cin>>t;
	for(int testcase=0; testcase<t; testcase++){
		cin>>expression;
		cout<<reversePolishNotation(expression)<<"\n";
	}
	return 0;
}