import java.math.BigDecimal;
import java.util.Scanner;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**

• Description: TODO 题目描述

• 输入一个表达式（用字符串表示），求这个表达式的值。

• 保证字符串中的有效字符包括[‘0’-‘9’],‘+’,‘-’, ‘*’,‘/’ ,‘(’， ‘)’,‘[’, ‘]’,‘{’ ,‘}’。且表达式一定合法。

• 输入描述: 输入一个算术表达式 输出描述: 得到计算结果

• 示例1 输入 3+2*{1+2*[-4/(8-6)+7]} 输出 25

• @title: Demo008

• Created by 19040838 on 2021.01.28 10:11
  /
  public class Demo008 {
  public static void main(String[] args) {
  String reg = "¹$";
  Scanner sc = new Scanner(System.in);
  while (sc.hasNext()) {
  String input = sc.nextLine().replace("[","(").replace("]",")")
  .replace("{","(").replace("}",")");
  if (!input.matches(reg)) {
  return;
  }
  System.out.println(arithmetic(input));
  }
  }

  public static double arithmetic(String exp){
  String result = parseExp(exp).replaceAll("[\[\]]", “”);
  return Double.parseDouble(exp);
  }
  /**

  • 解析计算四则运算表达式，例：2+((3+4)2-22)/23

  • @param expression

  • @return
    */
    public static String parseExp(String expression){
    //String numberReg="^((?!0)\d+(\.\d+(?<!0))?)|(0\.\d+(?<!0))KaTeX parse error: Got function '\newline' with no arguments as superscript at position 1: \̲n̲e̲w̲l̲i̲n̲e̲", “KaTeX parse error: Invalid size: '\newline-\newlined+(\newline.\newlined+)?\newline'”;
    //最小表达式计算
    if(expression.matches(minExp)){
    String result=calculate(expression);

     return Double.parseDouble(result)>=0?result:"["+result+"]";
    

    }
    //计算不带括号的四则运算
    String noParentheses="^[\(\)]+$";
    String priorOperatorExp="(((\d+(\.\d+)?)|(\[\-\d+(\.\d+)?\]))\*\/)";
    String operatorExp="(((\d+(\.\d+)?)|(\[\-\d+(\.\d+)?\]))\+\-)";
    if(expression.matches(noParentheses)){
    Pattern patt=Pattern.compile(priorOperatorExp);
    Matcher mat=patt.matcher(expression);
    if(mat.find()){
    String tempMinExp=mat.group();
    expression=expression.replaceFirst(priorOperatorExp, parseExp(tempMinExp));
    }else{
    patt=Pattern.compile(operatorExp);
    mat=patt.matcher(expression);

         if(mat.find()){
             String tempMinExp=mat.group();
             expression=expression.replaceFirst(operatorExp, parseExp(tempMinExp));
         }
     }
     return parseExp(expression);
    

    }
    //计算带括号的四则运算
    String minParentheses="\([^\(\)]+\)";
    Pattern patt= Pattern.compile(minParentheses);
    Matcher mat=patt.matcher(expression);
    if(mat.find()){
    String tempMinExp=mat.group();
    expression=expression.replaceFirst(minParentheses, parseExp(tempMinExp));
    }
    return parseExp(expression);
    }
    /**

  • 计算最小单位四则运算表达式（两个数字）

  • @param exp

  • @return
    /
    public static String calculate(String exp){
    exp=exp.replaceAll("[\[\]]", “”);
    String number[]=exp.replaceFirst("(\d)[\+\-\\/]", “$1,”).split(",");
    BigDecimal number1=new BigDecimal(number[0]);
    BigDecimal number2=new BigDecimal(number[1]);
    BigDecimal result=null;

    String operator=exp.replaceFirst("^.\d([\+\-\\/]).+$", “$1”);
    if("+".equals(operator)){
    result=number1.add(number2);
    }else if("-".equals(operator)){
    result=number1.subtract(number2);
    }else if("*".equals(operator)){
    result=number1.multiply(number2);
    }else if("/".equals(operator)){
    result=number1.divide(number2);
    }

    return result!=null?result.toString():null;
    }
    }

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1. 0-9*\-\[\]+/)(}{x22 ↩︎