【代码·Patten】theme: Calculator

Polish Calculator

Infix->Postfix Rules:

• number -> postfix stack
• ( -> opera stack
• ) -> pop opera stack until (
• +-*/ ->
  • pop greater or equal priority operators
  • push them to postfix stack
  • opera stack

class Solution {
public:
    int string2Int(const string s){
        int result=0;
        for(auto c:s){
            result=result*10-48+c;
        }
        return result;
    }

    vector<string> str2Vector(string s){
        vector<string> infix_tokens;
        string num;
        for(char c:s){
            if(c==' ') continue;
            if(c>47)    num=num+c;
            else{
                infix_tokens.push_back(num);
                num = c;
                infix_tokens.push_back(num);
                num = "";
            }
        }
        infix_tokens.push_back(num);    //last num
        for(int i=0;i<infix_tokens.size();i++){
            cout<<infix_tokens[i]<<" ";
        }
        cout<<endl;
        return infix_tokens;
    }

    stack<string> infix2Post(vector<string> infix_tokens){
        stack<string> postfix_tokens;
        stack<string> opera;
        for(auto token:infix_tokens){
            if(token =="(") opera.push("(");
            else if(token==")"){
                while(!opera.empty()&&opera.top()!="("){
                    postfix_tokens.push(opera.top());
                    opera.pop();
                }
                opera.pop();    //"("
            }
            else if(token=="+"||token=="-"||token=="*"||token=="/"){
                if(token=="+"||token=="-"){
                    while(!opera.empty()&&opera.top()!="("){
                        postfix_tokens.push(opera.top());
                        opera.pop();
                    }
                    opera.push(token);
                }
                else{
                    while(!opera.empty()&&(opera.top()=="*"||opera.top()=="/")){
                        postfix_tokens.push(opera.top());
                        opera.pop();
                    }
                    opera.push(token);
                }
            }
            else
                postfix_tokens.push(token); //num
        }
        while(!opera.empty()){      //leftover
            postfix_tokens.push(opera.top());
            opera.pop();
        }
        return postfix_tokens;
    }

    int evalPostfix(stack<string> &postfix_tokens){
        int value = 0;
        if(!postfix_tokens.empty()){
            string opera = postfix_tokens.top();
            cout<<"opera: "<<opera<<endl;
            if(opera == "+"){
                postfix_tokens.pop();
                int second = evalPostfix(postfix_tokens);
                int first = evalPostfix(postfix_tokens);
                cout<<first<<" + "<<second<<endl;       //test
                return first + second;
            }
            else if(opera == "-"){
                postfix_tokens.pop();
                int second = evalPostfix(postfix_tokens);
                int first = evalPostfix(postfix_tokens);
                cout<<first<<" - "<<second<<endl;       //test
                return first - second;
            }
            else if(opera == "*"){
                postfix_tokens.pop();
                int second = evalPostfix(postfix_tokens);
                int first = evalPostfix(postfix_tokens);
                cout<<first<<" * "<<second<<endl;       //test
                return first * second;
            }
            else if(opera == "/"){
                postfix_tokens.pop();
                int second = evalPostfix(postfix_tokens);
                int first = evalPostfix(postfix_tokens);
                cout<<first<<" / "<<second<<endl;       //test
                return first / second;
            }
            else//num
            {
                int num = string2Int(opera);
                postfix_tokens.pop();
                cout<<"num: "<<num<<endl;   //test
                return num;
            }
        }
        else
        {
            cout<<"error 2"<<endl;
        }
        return 0;

    }
    int calculate(string s) {
        vector<string> infix_tokens = str2Vector(s);
        stack<string> postfix_tokens = infix2Post(infix_tokens);
        int result = evalPostfix(postfix_tokens);
        return result;
    }
};