CCF：201903-2二十四点(JAVA版)

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

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();
        scanner.nextLine();
        while(n-->0) {
            char[] a = scanner.nextLine().toCharArray();
            if(value(a)==24) {
                System.out.println("Yes");
            }else {
                System.out.println("No");
            }
        }
    }

    private static int value(char[] a) {
        LinkedList<String> que = new LinkedList<>();
        int l = 0,r = 6;
        while(l<=r) {
            if(a[l]<='9'&&a[l]>='0') {//数字
                if(que.size()>0) {
                    String op = que.pollLast();
                    if(op.equals("x")||op.equals("/")) {
                        int num = Integer.parseInt(que.pollLast());
                        que.add(""+compute(num,op,a[l]-'0'));
                    }else {
                        que.add(op);
                        que.add(""+a[l]);
                    }
                }else {
                    que.add(""+a[l]);
                }
                l++;
            }else {//符号
                que.add(""+a[l++]);
            }
        }
        while(que.size()>1) {
            int na = Integer.parseInt(que.pollFirst());
            String op = que.pollFirst();
            int nb = Integer.parseInt(que.pollFirst());
            que.addFirst(""+compute(na, op, nb));
        }
        return Integer.parseInt(que.getFirst());
    }

    private static int compute(int num, String op, int i) {
        switch(op) {
        case "+": return num+i;
        case "-": return num-i;
        case "x": return num*i;
        case "/": return num/i;
        }
        return 0;
    }
}

10
9+3+4x3
5+4x5x5
7-9-9+8
5x6/5x4
3+5+7+9
1x1+9-9
1x9-5/9
8/5+6x9
6x7-3x6
6x4+4/5