hdu 1325

Is It A Tree?

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 27685    Accepted Submission(s): 6390

Problem Description

A tree is a well-known data structure that is either empty (null, void, nothing) or is a set of one or more nodes connected by directed edges between nodes satisfying the following properties.
There is exactly one node, called the root, to which no directed edges point.

Every node except the root has exactly one edge pointing to it.

There is a unique sequence of directed edges from the root to each node.

For example, consider the illustrations below, in which nodes are represented by circles and edges are represented by lines with arrowheads. The first two of these are trees, but the last is not.



In this problem you will be given several descriptions of collections of nodes connected by directed edges. For each of these you are to determine if the collection satisfies the definition of a tree or not.

 

Input

The input will consist of a sequence of descriptions (test cases) followed by a pair of negative integers. Each test case will consist of a sequence of edge descriptions followed by a pair of zeroes Each edge description will consist of a pair of integers; the first integer identifies the node from which the edge begins, and the second integer identifies the node to which the edge is directed. Node numbers will always be greater than zero.

 

Output

For each test case display the line ``Case k is a tree." or the line ``Case k is not a tree.", where k corresponds to the test case number (they are sequentially numbered starting with 1).

 

Sample Input

6 8 5 3 5 2 6 4 5 6 0 0 8 1 7 3 6 2 8 9 7 5 7 4 7 8 7 6 0 0 3 8 6 8 6 4 5 3 5 6 5 2 0 0 -1 -1

 

Sample Output

Case 1 is a tree. Case 2 is a tree. Case 3 is not a tree.

 

Source

North Central North America 1997

 

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题意：
        给你一些边，看是否能成为一棵树

思路：
        原来想用并查集的，无奈不知数据范围（不给数据范围的都没屁眼），所以只能用树的范围做一波，树的性质：每条边只能有一个父亲结点，点数为边数加一。

code:
        

#include<string.h>
#include<iostream>
#include<algorithm>
#include<vector>
#include<stdio.h>
using namespace std;
const int N = 100010;
int flag[N], father[N];
void Init()
{
	for (int i = 0; i <= 1000; i++)
		father[i] = i,flag[i]=0;
}
int Find(int x)
{
	if (x != father[x])
		father[x] = Find(father[x]);
	return father[x];
}
void Merge(int a, int b)
{
	int p = Find(a);
	int q = Find(b);
	if (p > q)
		father[p] = q;
	else
		father[q] = p;
}
int main()
{
	int t = 0;
	int a, b;
	while (++t)
	{
		int n=0, m=0,ans=0;
		memset(father, 0, sizeof(father));
		while (1)
		{
			scanf("%d%d", &a, &b);
			if (a < 0)
				return 0;
			if (a == 0)
				break;
			if (!father[a])
				n++;
			if (!father[b])
				n++;
			if (father[b] == 2)
				ans = 1;
			if (father[a] != 2)
				father[a] = 1;
			father[b] = 2;
			m++;
		}
		if (n == m + 1 && !ans)
			printf("Case %d is a tree.\n", t);
		else
			printf("Case %d is not a tree.\n", t);
	}
	return 0;
}