evaluate-reverse-polish-notation.cc

// Evaluate Reverse Polish Notation
class Solution {
public:
  int evalRPN(vector<string> &tokens) {
    stack<int> st;
    int x, y;
    for (auto &s: tokens)
      if ('0' <= s[0] && s[0] <= '9' || s[0] == '-' && s.size() > 1)
        st.push(atoi(s.c_str()));
      else {
        y = st.top(); st.pop();
        x = st.top(); st.pop();
        switch (s[0]) {
        case '+':
          st.push(x+y);
          break;
        case '-':
          st.push(x-y);
          break;
        case '*':
          st.push(x*y);
          break;
        case '/':
          st.push(x/y);
          break;
        }
      }
    return st.top();
  }
};