Competitive-Programming/Basic calculator.cpp at main · Yosef-6/Competitive-Programming · GitHub

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//not an efficent soln two pass is made
class Solution {
public:
    int calculate(string s) {
    deque<string>mstack;
    char  op = '.'; // starting point
    stringstream ss;
    int j=0;

    while(j < s.size()){
        if(s[j] == '+' || s[j] == '-'){
            op = s[j];
            ss<<s[j];
            mstack.push_back(ss.str());
            ss.clear(); ss.str(string(""));
            j++;
        }
        else if(s[j]=='/' || s[j]== '*'){
            op = s[j];
            j++;
        }
        else if(s[j] != ' '){

            while(j < s.size() && (s[j] != '+' && s[j] != '-' && s[j] != '*' && s[j] != '/' && s[j] != ' '))
                ss<<s[j++];

            if(op == '*' || op == '/'){
                int op2;
                int op1;
                ss>>op2;
                ss.clear(); ss.str(string(""));
                ss<<mstack.back();
                ss>>op1;
                mstack.pop_back();
                ss.clear(); ss.str(string(""));
                ss<< (op == '/' ?   op1/op2   :   op1*op2);
                mstack.push_back(ss.str());
                ss.clear(); ss.str(string(""));
            }
            else{
                  mstack.push_back(ss.str());
                  ss.clear(); ss.str(string(""));
                }

        }
        else
            j++;

    }

    int result = 0;

    while(mstack.size()!=1){
            char fop = ' ';
            int op1;
            int op2;
            ss<<mstack.front();mstack.pop_front();fop = mstack.front()[0];mstack.pop_front();
            ss>>op1;ss.clear(); ss.str(string(""));
            ss<<mstack.front();
            ss>>op2;ss.clear(); ss.str(string(""));;mstack.pop_front();

            ss<< (fop == '+' ? op1 + op2 : op1 - op2 );
            mstack.push_front(ss.str());
            ss.clear(); ss.str(string(""));

    }
    ss<<mstack.back();
    ss>>result;


     return result;


    }
};

// one pass soln