题解 | #四则运算#

import java.util.Scanner;
import java.util.Stack;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        while (sc.hasNext()) {
            String line = sc.nextLine();
            line = line.replaceAll("\\{", "(");
            line = line.replaceAll("}", ")");
            line = line.replaceAll("\\[", "(");
            line = line.replaceAll("]", ")");
            System.out.println(resolve(line));
        }
        sc.close();
    }

    private static int resolve(String line) {
        char[] chars = line.toCharArray();
        int length = chars.length;
        Stack<Integer> stack = new Stack<>();
        stack.push(0);
        int number = 0;
        char sign = '+';
        for (int i = 0; i < length; i++) {
            char c = chars[i];
            if (c == ' ') {
                continue;
            }
            if (Character.isDigit(c)) {
                number = number * 10 + c - '0';
            }
            if (c == '(') {
                int j = i + 1;
                int count = 1;
                while (count > 0) {
                    if (chars[j] == ')') {
                        count--;
                    }
                    if (chars[j] == '(') {
                        count++;
                    }
                    j++;
                }
                number = resolve(line.substring(i + 1, j - 1));
                i = j - 1;
            }
            if (!Character.isDigit(c) || i == length - 1) {
                if (sign == '+') {
                    stack.push(number);
                } else if (sign == '-') {
                    stack.push(-1 * number);
                } else if (sign == '*') {
                    stack.push(stack.pop() * number);
                } else if (sign == '/') {
                    stack.push(stack.pop() / number);
                }
                sign = c;
                number = 0;
            }
        }
        int sum = 0;
        while (!stack.isEmpty()) {
            sum += stack.pop();
        }
        return sum;
    }
}