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;
        }
    }

补充一个python的实现：

 import math
 class Solution:
     def __init__(self):
         self.symbollist = set()
         self.symbollist.add('+')
         self.symbollist.add('-')
         self.symbollist.add('*')
         self.symbollist.add('/')

     def isSymbol(self,string):
         if string in self.symbollist:
             return True
         else:
             return False
     def cal(self,num1,num2,sym):
         if sym == '+':
             return num1 + num2
         elif sym == '-':
             return num2 - num1
         elif sym == '*':
             return num1 * num2
         else:
             dd = num2 / num1
             if dd < :
                 dd = math.ceil(dd)
             else:
                 dd = math.floor(dd)
             return dd

     def evalRPN(self, tokens: 'List[str]') -> int:
         numstack = []
         r =
         for s in tokens:
             if self.isSymbol(s):
                 num1 = numstack.pop(-)
                 num2 = numstack.pop(-)
                 r = self.cal(num1,num2,s)
                 numstack.append(r)
             else:
                 numstack.append(int(s))
         return numstack[]