Solution.cs

using System.Collections.Generic;

public class Solution {
    public int EvalRPN(string[] tokens) {
        var stack = new Stack<int>();
        foreach (var token in tokens)
        {
            switch (token)
            {
                case "+":
                    stack.Push(stack.Pop() + stack.Pop());
                    break;
                case "-":
                    stack.Push(-stack.Pop() + stack.Pop());
                    break;
                case "*":
                    stack.Push(stack.Pop() * stack.Pop());
                    break;
                case "/":
                    var right = stack.Pop();
                    stack.Push(stack.Pop() / right);
                    break;
                default:
                    stack.Push(int.Parse(token));
                    break;
            }
        }
        return stack.Pop();
    }
}