150.cpp

// stack-20ms.cpp
class Solution {
  public:
    int evalRPN(vector<string>& tokens) {
        stack<int> nums;
        for (auto& s : tokens) {
            if (s[s.size() - 1] >= '0' && s[s.size() - 1] <= '9')
                nums.push(stoi(s));
            else {
                auto n2 = nums.top();
                nums.pop();
                auto n1 = nums.top();
                nums.pop();
                switch (s[0]) {
                case '+':
                    nums.push(n1 + n2);
                    break;
                case '-':
                    nums.push(n1 - n2);
                    break;
                case '*':
                    nums.push(n1 * n2);
                    break;
                case '/':
                    nums.push(n1 / n2);
                    break;
                }
            }
        }
        return nums.top();
    }
};