150. Evaluate Reverse Polish Notation

解題心得

很經典的 stack 題目

程式碼

class Solution {
public:
    int evalRPN(vector<string>& tokens) {
        stack<int> st;
        for(int i=0; i<tokens.size(); i++)
        {
            if(tokens[i] == "+" || tokens[i] == "-" || tokens[i] == "*" || tokens[i] == "/")
            {
                int second = st.top(); st.pop();
                int first = st.top(); st.pop();
                if(tokens[i] == "+") st.push(first + second);
                else if(tokens[i] == "-") st.push(first - second);
                else if(tokens[i] == "*") st.push(first * second);
                else if(tokens[i] == "/") st.push(first / second);
            }
            else
            {
                st.push(stoi(tokens[i]));
            }
        }
        return st.top();
    }
};