leetcode Evaluate Reverse Polish Notation(计算逆波兰表达式)
题目要求:Evaluatethevalueofanarithmeticexpressionin ReversePolishNotation.Validoperatorsare +, -, *, /.Eachoperandmaybeanintegeroranotherexpression.Someexamples:["2","1","+","3","*"]->((2+1)*3)->9
["4","1