leetcode150

public class Solution
    {
        public int EvalRPN(string[] tokens)
        {
            Stack<int> ST_NUM = new Stack<int>();
            foreach (var to in tokens)
            {
                if (to == "+" || to == "-" || to == "*" || to == "/")
                {
                    var num1 = ST_NUM.Pop();
                    var num2 = ST_NUM.Pop();
                    if (to == "+")
                    {
                        var num = num2 + num1;
                        ST_NUM.Push(num);
                    }
                    else if (to == "-")
                    {
                        var num = num2 - num1;
                        ST_NUM.Push(num);
                    }
                    else if (to == "*")
                    {
                        var num = num2 * num1;
                        ST_NUM.Push(num);
                    }
                    else if (to == "/")
                    {
                        var num = num2 / num1;
                        ST_NUM.Push(num);
                    }
                }
                else
                {
                    var num = Convert.ToInt32(to);
                    ST_NUM.Push(num);
                }
            }
            var result = ST_NUM.Pop();
            return result;
        }
    }