OpenJudge

 1 #include <iostream>
 2 #include <cstring>
 3 #include <cmath>
 4 using namespace std;
 5 const double x = 1e-6;
 6 
 7 double a[5];
 8 
 9 bool dfs(int step)
10 {
11     int i,j,k,t;
12     if(step == 1)
13     {
14         if(fabs(a[0]-24)< x)
15             return 1;
16         else
17             return 0;
18     }
19     else
20     {
21         double m,n;
22         for(i=0;i<step;i++)
23             for(j=i+1;j<step;j++)
24             {
25                 m = a[i],n = a[j];
26                 a[j] = a[step - 1]; 
27                 for(k=1;k<=6;k++)
28                 {
29                    // m = a[i],n = a[j];
30                    // a[j] = a[step - 1]; 
31                     switch (k)
32                     {
33                         case 1:a[i] = m+n;
34                         if(dfs(step-1)) return 1;
35                         break;
36                         case 2:a[i] = m-n;
37                         if(dfs(step-1)) return 1;
38                         break;
39                         case 3:a[i] = n-m;
40                         if(dfs(step-1)) return 1;
41                         break;
42                         case 4:a[i] = m*n;
43                         if(dfs(step-1)) return 1;
44                         break;
45                         case 5:
46                             if(fabs(n)>=x)
47                             {   
48                                 a[i] = m/n;
49                                 if(dfs(step-1)) return 1;
50                                 break;
51                             }
52                         case 6:
53                             if(fabs(m)>=x)
54                             {   
55                                 a[i] = n/m;
56                                 if(dfs(step-1)) return 1;
57                                 break;
58                             }
59                     }
60                 }
61                 a[i] = m,a[j] = n;
62             }
63         }
64         return 0;//忘啦 
65 }
66             
67 int main()
68 {
69     int i,j,k,t;
70     while(1)
71     {
72         memset(a,0,sizeof(a));
73         double sum = 0;
74         for(i=0;i<4;i++)
75         {
76             cin>>a[i];
77             sum += a[i];
78         }
79         bool flag ;
80         if(0==sum)
81             break;
82         else 
83             flag = dfs(4);
84         if(flag)
85             cout<<"YES"<<endl;
86         else
87             cout<<"NO"<<endl;
88     }
89     return 0;
90 }