后缀表达式四则运算

import java.util.Stack;
public class Solution {
    public int evalRPN(String[] tokens) {
        Stack<Integer> stack=new Stack<Integer>();
        for (int i=0;i<tokens.length;i++){         
            try{//这里用捕捉异常的方式来处理非Int类型的符号，并单独处理，结构巧妙
                int num=Integer.parseInt(tokens[i]);
                stack.push(num);
            }  
            catch(Exception e){
                int b=stack.pop();
                int a=stack.pop();
                stack.push(get(a,b,tokens[i]));
            }
        }
        return stack.peek();
    }
        private int get(int a,int b,String operate){//利用switch,case选择分支结构完成四则运算
            switch(operate){
            case "+":
                return a+b;
            case"-":
                return a-b;
            case "*":
                return a*b;
            case "/":
                return a/b;
                default:
                    return 0;
        } 
    }
}

Evaluate the value of an arithmetic expression in Reverse Polish Notation.

Valid operators are+,-,*,/. Each operand may be an integer or another expression.

Some examples:

算法的思想就是，遍历数据，非符号压入堆栈，运算符就pop前两个整数，运算结束把结果放回堆栈。最终栈顶元素就是结果。