150. Evaluate Reverse Polish Notation.txt

https://leetcode.com/problems/evaluate-reverse-polish-notation/



class Solution {
private:
    int toInt(string a){
        int c = 0;
        if(a[0] == '-'){
            for(int i = 1; i < a.length(); i++){
                c += (a[i] - '0') * pow(10,a.length() - 1 - i);
            }
            return -1*c;
        }
        for(int i = 0; i < a.length(); i++){
            c += (a[i] - '0') * pow(10,a.length() - 1 - i);
        }
        return c;
    }
public:
    int evalRPN(vector<string>& tokens) {
        stack<int> st;
        int a,b;
        for(int i = 0; i < tokens.size(); i++){
            if(tokens[i] == "+"){
                a = st.top();st.pop();
                b = st.top();st.pop();
                st.push(a+b);
            }
            else if(tokens[i] == "-"){
                a = st.top();st.pop();
                b = st.top();st.pop();
                st.push(b-a);
            }
            else if(tokens[i] == "*"){
                a = st.top();st.pop();
                b = st.top();st.pop();
                st.push(b*a);
            }
            else if(tokens[i] == "/"){
                a = st.top();st.pop();
                b = st.top();st.pop();
                st.push(b/a);
            }
            else{
                a = toInt(tokens[i]);
                st.push(a);
            }
        }
        return st.top();
    }
};