题解 | #四则运算#

import java.util.Deque;
import java.util.LinkedList;
import java.util.Scanner;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        // 注意 hasNext 和 hasNextLine 的区别
        while (in.hasNextLine()) { // 注意 while 处理多个 case
            String s = in.nextLine();
            s = s.replace('[','(');
            s = s.replace('{','(');
            s=s.replace(']',')');
            s=s.replace('}',')');
            //System.out.println(s);
            Deque<Integer> numbers = new LinkedList<>();
            Deque<Character> operators = new LinkedList<>();
            int n = s.length();

            for (int i = 0 ; i < n ; ++i) {
                StringBuffer sb = new StringBuffer();

                while(i < n && s.charAt(i) >= '0' && s.charAt(i) <= '9') {
                    sb.append(s.charAt(i));
                    ++i;
                    //System.out.println(s.charAt(i));
                }
                //System.out.println(sb.toString());

                if(sb.length() > 0){

                    numbers.push(Integer.valueOf(sb.toString()));

                }
                

                if (i < n) {
                    char op = s.charAt(i);
                    if (op == '(') {
                        operators.push(op);
                    }

                    else if (op == '+' || op == '-') {
                        if(operators.isEmpty()){
                            operators.push(op);
                            continue;
                        }
                        char opPeak = operators.peek();
                        while (!operators.isEmpty() && operators.peek()!='(') {
                            int a = numbers.pop();
                            int b = numbers.pop();
                            if (opPeak == '*') {
                                numbers.push(a * b);
                            }
                            if (opPeak == '/') {
                                numbers.push(b / a);
                            }
                            if(opPeak == '+'){
                                numbers.push(b+a);
                            }
                            if(opPeak=='-'){
                                numbers.push(b-a);
                            }
                            operators.pop();
                            if(operators.isEmpty()){
                                break;
                            }
                            opPeak = operators.peek();

                        }
                        operators.push(op);
                    }

                    else if (op == '*' || op == '/') {
                        operators.push(op);
                    } else {
                        while (operators.peek() != '(') {
                            char opPeak = operators.pop();
                            
                            int a = numbers.pop();
                            int b = numbers.pop();
                            //System.out.println(a+" "+b);
                            //System.out.println(numbers);
                            //System.out.println(operators);
                            if (opPeak == '+') {
                                numbers.push(a + b);
                            } else if (opPeak == '-') {
                                numbers.push(b - a);
                            } else if (opPeak == '*') {
                                numbers.push(a * b);
                            } else {
                                numbers.push(b / a);
                            }
                           
                            
                        }
                        operators.pop(); //把左括号出栈
                    }
                }

            }

            while (!operators.isEmpty()) {
                int a = numbers.pop();
                int b = numbers.pop();
                char op = operators.pop();
                if (op == '+') {
                    numbers.push(a + b);
                } else if (op == '-') {
                    numbers.push(b - a);
                } else if (op == '*') {
                    numbers.push(a * b);
                } else {
                    numbers.push(b / a);
                }
            }
            System.out.println(numbers.peek());
        }
    }
}