该题考察表达式计算，可以用Stack实现

具体代码

java">import java.util.*;

public class Main7 {

    public static Map<Character,Integer> map = new HashMap<>();

    public static boolean isOp(char c){
        if(c=='+' || c=='-' ||c=='x' ||c=='/'){
            return true;
        }
        else{
            return false;
        }
    }

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int num = sc.nextInt();
        sc.nextLine();
        List<String> exprLst = new ArrayList<>();
        for(int i = 0; i < num; i++){
            String expr = sc.nextLine();
            exprLst.add(expr);
        }


        map.put('+',1);
        map.put('-',1);
        map.put('x',2);
        map.put('/',2);

//        String expr = "1x1+9-9";
        for(String expr : exprLst){
            StringBuilder sb = new StringBuilder();
            Stack<Character> stack = new Stack<>();
            Stack<String> compStack = new Stack<>();

            char[] arr = expr.toCharArray();
            for(char c : arr){
                if(!isOp(c)){
                    sb.append(c);
                }
                else
                {
                    if(stack.isEmpty()){
                        stack.push(c);
                    }
                    else{
                        if(map.get(c) > map.get(stack.peek())){
                            stack.push(c);
                        }
                        else{
                            while (!stack.isEmpty() && map.get(c) <= map.get(stack.peek())){
                                char op = stack.pop();
                                sb.append(op);
                            }
                            stack.push(c);
                        }
                    }

                }
            }

            while (!stack.isEmpty()){
                sb.append(stack.pop());
            }
//            System.out.println(sb);

            char[] postArr = sb.toString().toCharArray();
            for(char c : postArr){
                if(!isOp(c)){
                    compStack.push(String.valueOf(c));
                }
                else{
                    int b = Integer.parseInt(compStack.pop());
                    int a = Integer.parseInt(compStack.pop());
                    switch (c){
                        case '+':
                            compStack.push(String.valueOf(a+b));
                            break;
                        case '-':
                            compStack.push(String.valueOf(a-b));
                            break;
                        case 'x':
                            compStack.push(String.valueOf(a*b));
                            break;
                        case '/':
                            compStack.push(String.valueOf(a/b));
                            break;
                        default:
                            break;
                    }
                }
            }
//            System.out.println(compStack.pop());
            if(Integer.parseInt(compStack.pop()) == 24){
                System.out.println("Yes");
            }
            else{
                System.out.println("No");
            }
        }

    }
}