33. Evaluate Reverse Polish Notation

class Solution:
    def evalRPN(self, tokens: List[str]) -> int:
        stack = []
        for tok in tokens:
            if tok in '+-*/' and len(tok) == 1:
                b, a = stack.pop(), stack.pop()      # note the order: a op b
                if tok == '+': stack.append(a + b)
                elif tok == '-': stack.append(a - b)
                elif tok == '*': stack.append(a * b)
                else: stack.append(int(a / b))       # truncate toward zero
            else:
                stack.append(int(tok))
        return stack[-1]

class Solution {
    public int evalRPN(String[] tokens) {
        Deque<Integer> stack = new ArrayDeque<>();
        for (String tok : tokens) {
            switch (tok) {
                case "+" -> stack.push(stack.pop() + stack.pop());
                case "*" -> stack.push(stack.pop() * stack.pop());
                case "-" -> { int b = stack.pop(), a = stack.pop(); stack.push(a - b); }
                case "/" -> { int b = stack.pop(), a = stack.pop(); stack.push(a / b); }
                default -> stack.push(Integer.parseInt(tok));
            }
        }
        return stack.pop();
    }
}

class Solution {
public:
    int evalRPN(vector<string>& tokens) {
        vector<long long> st;
        for (const string& tok : tokens) {
            if (tok.size() == 1 && string("+-*/").find(tok[0]) != string::npos) {
                long long b = st.back(); st.pop_back();
                long long a = st.back(); st.pop_back();
                if (tok == "+") st.push_back(a + b);
                else if (tok == "-") st.push_back(a - b);
                else if (tok == "*") st.push_back(a * b);
                else st.push_back(a / b);          // C++ division truncates toward zero
            } else st.push_back(stoll(tok));
        }
        return (int)st.back();
    }
};

function evalRPN(tokens) {
  const stack = [];
  for (const tok of tokens) {
    if (['+', '-', '*', '/'].includes(tok)) {
      const b = stack.pop(), a = stack.pop();
      stack.push(tok === '+' ? a + b : tok === '-' ? a - b : tok === '*' ? a * b : Math.trunc(a / b));
    } else stack.push(Number(tok));
  }
  return stack.pop();
}