《并查集》hdoj acm 5.1.2

#include <stdio.h>

const int max_num = 100000+10;
typedef struct
{
int num,root,conn;
}Node;

Node node[max_num];

void init()
{
for(int i = 0; i < max_num; i++)
{
node[i].conn = 0;
node[i].root= i;
node[i].num=0;
}
}

int find_root(int a)
{
if(node[a].root!=a)
return node[a].root = find_root(node[a].root);
return node[a].root;
}

void union_set(int a,int b)
{
a = find_root(a);
b = find_root(b);
if(a==b)
return;
node[b].root=a;
}

int main()
{
int n,m;
int i = 1;
bool flag=true;
init();
while(scanf("%d%d",&n,&m)!=EOF&&n>=0&&m>=0)
{
if(!flag&&n!=0&&n!=0)continue;
if(n==0&&m==0)
{
int root_num=0;
for(int j = 1; j < max_num;j++)
{
if(node[j].num && find_root(j)==j)
root_num++;
if(node[j].conn>1)
{
flag = false;
break;
}
}
if(root_num>1)
flag=false;
if(flag)
printf("Case %d is a tree.\n",i++);
else printf("Case %d is not a tree.\n",i++);
flag = true;
init();
continue;
}
if(m!=n&&find_root(n)==find_root(m))
flag = false;
else
{
node[m].num = 1;
node[n].num = 1;
node[m].conn++;
union_set(n,m);
}
}
return 0;
}