藍橋杯-算法訓練-前綴表達式

沒有用棧，前綴還是可以直接用正則的

import java.util.*;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String expression = scanner.nextLine();
        scanner.close();

        System.out.println(getResult(expression));
    }

    private static String getResult(String expression) {
        Pattern pattern = Pattern.compile("([\\+\\-\\*/]) (\\d+) (\\d+)");
        Matcher matcher;
        while (true) {
            matcher = pattern.matcher(expression);
            if (!matcher.find()) {
                break;
            }

            char op = matcher.group(1).charAt(0);
            int n1 = Integer.parseInt(matcher.group(2));
            int n2 = Integer.parseInt(matcher.group(3));
            expression = expression.replace(matcher.group(0), String.valueOf(getResult(op, n1, n2)));
        }
        return expression;
    }

    private static int getResult(char op, int n1, int n2) {
        switch (op) {
            case '*':
                return n1 * n2;
            case '+':
                return n1 + n2;
            case '-':
                return n1 - n2;
            case '/':
                return n1 / n2;
        }
        return -1;
    }

}