hdu 1325 Is It A Tree?

http://acm.hdu.edu.cn/showproblem.php?pid=1325

  1 #include <cstdio>

  2 #include <cstring>

  3 #include <algorithm>

  4 #define maxn 5000

  5 using namespace std;

  6 

  7 int in[maxn],f[maxn];

  8 bool ha[maxn];

  9 int max1;

 10 

 11 struct node

 12 {

 13     int u,v;

 14 }p[maxn*4];

 15 

 16 void inti()

 17 {

 18     for(int i=1; i<=max1; i++)

 19     {

 20         f[i]=i;

 21     }

 22 }

 23 

 24 int find1(int x)

 25 {

 26     if(x==f[x]) return x;

 27     return f[x]=find1(f[x]);

 28 }

 29 

 30 void union1(int a,int b)

 31 {

 32     int fa=find1(a);

 33     int fb=find1(b);

 34     if(fa!=fb)

 35     {

 36         f[fb]=fa;

 37     }

 38 }

 39 

 40 int main()

 41 {

 42     int case1=1;

 43     while(scanf("%d%d",&p[0].u,&p[0].v)!=EOF)

 44     {

 45         if(p[0].u<0||p[0].v<0) break;

 46         if(p[0].u==0&&p[0].v==0)

 47         {

 48             printf("Case %d is a tree.\n",case1++);

 49             continue;

 50         }

 51         memset(in,0,sizeof(in));

 52         memset(ha,false,sizeof(ha));

 53         max1=0;

 54         max1=max(max1,p[0].u);

 55         max1=max(max1,p[0].v); 

 56         ha[p[0].u]=ha[p[0].v]=true;

 57         in[p[0].v]++;

 58         int m=1;

 59         while(scanf("%d%d",&p[m].u,&p[m].v))

 60         {

 61             if(p[m].u==0&&p[m].v==0) break;

 62             in[p[m].v]++;

 63             ha[p[m].u]=ha[p[m].v]=true;

 64             max1=max(max1,p[m].u);

 65             max1=max(max1,p[m].v);

 66             m++;

 67         }

 68         bool flag1=false;

 69         int m1=0;

 70         for(int i=1; i<=max1; i++)

 71         {

 72             if(ha[i]&&in[i]>1)

 73             {

 74                 flag1=true;

 75                 break;

 76             }

 77         }

 78         for(int i=1; i<=max1; i++)

 79         {

 80             if(ha[i]&&in[i]==0) m1++;

 81         }

 82         if(flag1||m1!=1)

 83         {

 84              printf("Case %d is not a tree.\n",case1++);

 85              continue;

 86         }

 87         inti();

 88         for(int i=0; i<m; i++)

 89         {

 90             union1(p[i].u,p[i].v);

 91         }

 92         int ans=0;

 93         for(int i=1; i<=max1; i++)

 94         {

 95             if(ha[i]&&f[i]==i) ans++;

 96         }

 97         if(ans!=1) printf("Case %d is not a tree.\n",case1++);

 98         else

 99             printf("Case %d is a tree.\n",case1++);

100     }

101     return 0;

102 }

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