pku1308.cpp

这是ACM 方面的资料 是PKU的 北京大学的出来的

#include <stdio.h>

int st[100];

int getid(int x)
{
	int root;
	if (st[x] == x)
	{
		return x;
	}

	root = getid(st[x]);
	st[x] = root;
	return root;
}

int main()
{
	int s, e, i, l, istree, t = 0, totalid;

	
	while (scanf("%d%d", &s, &e) != -1)
	{
		t++;
		istree = 1;
		for (i = 0; i < 100; i++)
		{
			st[i] = -1;
		}
		
		if (s == -1 && e == -1)
		{
			break;
		}

		if (s == 0 && e == 0)
		{
			printf("Case %d is a tree.\n", t);
			continue;
		}
		st[e] = e;
		st[s] = s;
		if (s == e)
		{
			istree = 0;
		}
		totalid = 2;
		st[e] = s;
		
		l = 1;

		while (scanf("%d %d", &s, &e) != -1)
		{
			if (s == 0 && e == 0)
			{
				break;
			}
			l++;
			if (st[s] == -1)
			{
				st[s] = s;
				totalid++;
			}
			if (st[e] == -1)
			{
				st[e] = e;
				totalid++;
			}
			if (getid(s) == getid(e))
			{
				istree = 0;
			}
			else st[getid(e)] = getid(s);
		}

		if (istree == 1 && l + 1 == totalid)
		{
			printf("Case %d is a tree.\n", t);
		}
		else
		{
			printf("Case %d is not a tree.\n", t);
		}
	}
	return 0;
}