暑假集训(2)第一弹 -----Is It A Tree?（Poj308)

 1 #include "cstdio"
 2 struct node
 3 {
 4     int i;
 5     int j;
 6 };
 7 node a[1000],b[1000];
 8 int number,time=0;
 9 int nbegin()
10 {
11    int i=0;
12    time++;
13    while (scanf ("%d%d",&a[i].i,&a[i].j)&& (a[i].i != -1 || a[i].j != -1))
14    {
15        number = i;
16        if (a[i].i || a[i].j)
17              i++;
18        else
19            return 1;
20    }
21    return 0;
22 }
23 void tree()
24 {
25    int now,next,q;
26    node y;
27    if (a[number].i == 0 && a[number].j == 0 && number == 0)
28     {
29             printf ("Case %d is a tree.\n",time);
30             return;
31     }
32     for (int i=0;i<number;i++)
33     {
34          for (int k=0;k<number;k++)
35         {
36          if (a[i].j == a[k].j && i != k)
37             {
38                 printf("Case %d is not a tree.\n",time);
39                 return;
40             }
41          if (a[i].i == a[k].j && a[i].j == a[k].i)
42              {
43                 printf("Case %d is not a tree.\n",time);
44                 return;
45              }
46         }
47     }
48    for (int i=0;i<number;i++)
49    {
50         now=0;
51         next=0;
52         q=0;
53       for (int t=0;t<number;t++)
54         if (a[t].i == a[i].i )
55         {
56           b[next++] = a[t];
57           q++;
58         }
59       while (next != now)
60             {
61               y = b[now];
62               now++;
63               for (int j=0;j<number;j++)
64                 if (y.j == a[j].i && y.i != a[j].j)
65                 {
66                         b[next++] = a[j];
67                         q++;
68                 }
69             }
70         if (q == number)
71         {
72                 printf ("Case %d is a tree.\n",time);
73                 return;
74         }
75     }
76      printf("Case %d is not a tree.\n",time);
77 }
78 int main()
79 {
80     while(nbegin())
81         tree();
82     return 0;
83 }