计算后缀表达式

应用：逆波兰表达式（后缀表达式），使用单个栈就行。

package com.linzhongkai.stack;
import java.util.LinkedList;
import java.util.Scanner;
public class CalcPostExp {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String string = scanner.nextLine();
        String[] tokens = string.split(" ");
        System.out.println(calcPostExp(tokens));
    }
    public static int calcPostExp(String[] tokens) {
        LinkedList<Integer> stack = new LinkedList<>();
        for(String t : tokens) {
            if (t.equals("+")) {
                int num1 = stack.removeLast();
                int num2 = stack.removeLast();
                stack.addLast(num1+num2);
            } else if (t.equals("-")) {
                int num1 = stack.removeLast();
                int num2 = stack.removeLast();
                stack.addLast(num2-num1);
            } else if (t.equals("*")) {
                int num1 = stack.removeLast();
                int num2 = stack.removeLast();
                stack.addLast(num1*num2);
            } else if (t.equals("/")) {
                int num1 = stack.removeLast();
                int num2 = stack.removeLast();
                stack.addLast(num2/num1);
            } else {
                stack.addLast(Integer.valueOf(t));
            }
        }
        if (stack.isEmpty()) {
                throw new RuntimeException();
        }
        return stack.pollLast();
    }
}