55555

package ex205.exp;

import java.util.Stack;

public class ArithmeticExpression {
    private String expr;

    public ArithmeticExpression(String expr) {
        this.expr = expr;
    }

    public int getResult() {
        Stack<Integer> operandStack = new Stack<>();
        Stack<String> operatorStack = new Stack<>();

        String[] tokens = expr.split("\\s+");

        for (String token : tokens) {
            if (isNumber(token)) {
                operandStack.push(Integer.parseInt(token));
            } else if (token.equals("(")) {
                operatorStack.push(token);
            } else if (token.equals(")")) {
                while (!operatorStack.peek().equals("(")) {
                    performOperation(operandStack, operatorStack);
                }
                operatorStack.pop();
            } else if (isOperator(token)) {
                while (!operatorStack.isEmpty() && precedence(token) <= precedence(operatorStack.peek())) {
                    performOperation(operandStack, operatorStack);
                }
                operatorStack.push(token);
            }
        }

        while (!operatorStack.isEmpty()) {
            performOperation(operandStack, operatorStack);
        }

        return operandStack.pop();
    }

    private boolean isNumber(String token) {
        try {
            Integer.parseInt(token);
            return true;
        } catch (NumberFormatException e) {
            return false;
        }
    }

    private boolean isOperator(String token) {
        return token.equals("+") || token.equals("-") || token.equals("*") || token.equals("/");
    }

    private int precedence(String operator) {
        if (operator.equals("+") || operator.equals("-")) {
            return 1;
        } else if (operator.equals("*") || operator.equals("/")) {
            return 2;
        } else {
            return 0;
        }
    }

    private void performOperation(Stack<Integer> operandStack, Stack<String> operatorStack) {
        int num2 = operandStack.pop();
        int num1 = operandStack.pop();
        String operator = operatorStack.pop();

        int result = 0;
        switch (operator) {
            case "+":
                result = num1 + num2;
                break;
            case "-":
                result = num1 - num2;
                break;
            case "*":
                result = num1 * num2;
                break;
            case "/":
                result = num1 / num2;
                break;
        }
        operandStack.push(result);
    }
}

package ex205;

import ex205.exp.ArithmeticExpression;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入一个符合整数算术四则运算表达式的字符串：(运算数和运算符号之间以空格隔开)");
        String expression = scanner.nextLine();
        ArithmeticExpression arithmeticExpression = new ArithmeticExpression(expression);
        int result = arithmeticExpression.getResult();
        System.out.println(result);
        scanner.close();
    }
}