逆波兰计算器

package com.dai.stack;

import java.util.List;
import java.util.ArrayList;
import java.util.Stack;

import javax.sql.rowset.JoinRowSet;
import javax.swing.text.AbstractDocument.BranchElement;
public class PolandNotation {

    public static void main(String[] args) {
        //将中缀表达式转后缀表达式
        //直接扫描字符串不方便，不妨先将字符串转化成中缀对应的List
        
        String expression = "1+((2+3)*4)-5";
        List<String> infixExpressionList = toInfixExpressionList(expression);
        System.out.println("中缀表达式对应的List" + infixExpressionList);
        List<String> parseSuffixExpressionList = parseSuffixExpressionList(infixExpressionList);
        System.out.println("后缀表达式对应的list:"+ parseSuffixExpressionList);
        System.out.println(expression+ "=" + calculate(parseSuffixExpressionList));
    
    }
        //定义一个逆波兰表达式
        //(3+4)*5-6
        /*String suffixExpression  = "3 4 + 5 * 6 -";
        //
        List<String> rpnList = getListString(suffixExpression);
        System.out.println("rpnList" + rpnList);
        
        int res = calculate(rpnList);
        System.out.println("计算的结果是=" + res);
     }
     
    //将中缀表达式转化成对应的List*/
    
    //将中缀List转为后缀List
    public static List<String> parseSuffixExpressionList(List<String> ls){
        //定义两个栈
        Stack<String> s1 = new Stack<String>(); //符号栈
        //s2在整个过程中没有pop操作，还要逆序输出，直接用List 替代更好
        //Stack<String> s2 = new Stack<String>(); //存中间结果的栈
        List<String> s2 = new ArrayList<String>();
        //遍历ls
        for(String item : ls) {
            //如果是一个数，就加入到s2
            if(item.matches("\\d+")) {
                s2.add(item);
            }else if (item.equals("(")) {
                s1.push(item);
            }else if (item.equals(")")) {
                while (!s1.peek().equals("(")) {
                    s2.add(s1.pop());
                }
                s1.pop(); //将小括号弹出栈
            }else {
                //当item优先级<=栈顶的优先级，将s1栈顶弹出加入到s2
                while(s1.size() != 0 && Operation.getValue(s1.peek()) >= Operation.getValue(item)) {
                    s2.add(s1.pop());
                }
                //将item压入栈
                s1.push(item);
            }
        }
        while(s1.size() != 0) {
            s2.add(s1.pop());
        }
        return s2;
    }
    
    //将中缀转为List
    public static List<String> toInfixExpressionList(String s){
        List<String> ls = new ArrayList<String>();
        int i = 0; //指针，用于遍历字符串
        String str; //多位数拼接
        char c;
        do {
            //如果c非数字，则加入ls
            if((c=s.charAt(i))<48 || (c=s.charAt(i))>57) {
                ls.add(""+c);
                i++;
            }else{//考虑多位数
                str = "";
                while(i < s.length() && (c=s.charAt(i))>=48 && (c=s.charAt(i))<=57) {
                    str += c;
                    i++;
                }
                ls.add(str);
            }
        } while (i < s.length());
        return ls;
    }
    //将逆波兰表达式，依次将数据和运算符 放入到ArrayList中
    public static List<String> getListString(String suffixExpression){
        //将sufffixExpression 分割
        String[] split = suffixExpression.split(" ");
        List<String> list = new ArrayList<String>();
        for(String ele : split) {
            list.add(ele);
        }
        return list;
    }
    
    //完成对逆波兰表达式的计算
    public static int calculate(List<String> ls) {
        //创建一个栈即可
        Stack<String> stack = new Stack<String>();
        //遍历ls
        for(String item:ls) {
            //使用正则表达式取数
            if (item.matches("\\d+")) {//匹配的是多位数
                //入栈
                stack.push(item);
            }else {
                //pop出两个数，并运算，再入栈
                int num2 = Integer.parseInt(stack.pop());
                int num1 = Integer.parseInt(stack.pop());
                int res = 0;
                if(item.equals("+")) {
                    res = num1+num2;
                }else if (item.equals("-")) {
                    res = num1 - num2;
                }else if (item.equals("*")) {
                    res = num1 * num2;
                }else if (item.equals("/")) {
                    res = num1 / num2;
                }else {
                    throw new RuntimeException("运算符有误！");
                }
                stack.push(res+"");
            }
        }
        //最后留下来的就是结果
        return Integer.parseInt(stack.pop());
    }

}

//一个可以返回运算符优先级的类
class Operation{
    private static int ADD = 1;
    private static int SUB = 1;
    private static int MUL = 2;
    private static int DIV = 2;
    
    public static int getValue(String operation) {
        int result = 0;
        switch (operation) {
        case "+":
            result = ADD;
            break;
        case "-":
            result = SUB;
            break;
        case "*":
            result = MUL;
            break;
        case "/":
            result = DIV;
            break;
        default:
            //throw new RuntimeException("运算符非法");
            break;
        }
        return result;
    }
}