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 < 0:
                dd = math.ceil(dd)
            else:
                dd = math.floor(dd)
            return dd

    def evalRPN(self, tokens: 'List[str]') -> int:
        numstack = []
        r = 0
        for s in tokens:
            if self.isSymbol(s):
                num1 = numstack.pop(-1)
                num2 = numstack.pop(-1)
                r = self.cal(num1,num2,s)
                numstack.append(r)
            else:
                numstack.append(int(s))
        return numstack[0]