HDU 1325 Is It A Tree? 并查集判断是否成树

Is It A Tree?

Time Limit: 2000/1000 MS (Java/Others) Memory Limit: 65536/32768 K (Java/Others)Total Submission(s): 1123 Accepted Submission(s): 346 

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 45 6 0 08 1 7 3 6 2 8 9 7 57 4 7 8 7 6 0 03 8 6 8 6 45 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

题目大意：

给出有向图！！注意是有向图，然后问是否成树，有回路不行，并且只能有一个根节点。

思路：

和小希的迷宫差不多，只不过注意这个是  输入 小于0 的时候结束，，，超时了好久。。然后就是基本按照上题相同的方法就可以过了。

AC代码：

#include <iostream>#include<stdio.h>using namespace std;const int MAX = 1002;int n,m,k;int ans;int parent[MAX+10];bool vis[MAX+10];int GetParent(int a){     if( parent[a]!= a)        parent[a] = GetParent(parent[a]);     return parent[a];}void Merge(int a,int b){    int p1 = GetParent(a);    int p2 = GetParent(b);    if( p1 == p2 )    {        ans=0;        return;    }    if(p2!=b)    {        ans=0;        return;    }    parent[p2] = p1;}int main(){    int minn,maxx;    int cc=1;    while(true)    {        ans=1;        scanf("%d%d",&n,&m);        if( n <0 && m <0)            break;        minn=min(n,m);        maxx=max(n,m);        cout<<"Case "<<cc<<" ";        for(int i = 0;i <=MAX; ++i)        {            parent[i] = i;            vis[i]=0;        }        vis[n]=vis[m]=1;        Merge(n,m);        while(666)        {            scanf("%d%d",&n,&m);            if(n==0&&m==0)                break;            if(n<minn) minn=n;            if(m<minn) minn=m;            if(n>maxx) maxx=n;            if(m>maxx) maxx=m;            Merge(n,m);            vis[n]=vis[m]=1;        }        int work=0;        for(int i=minn;i<=maxx;i++)        {            if(GetParent(i)==i&&vis[i])                work++;            if(work>1)            {                ans=0;                break;            }        }        if(ans)            cout<<"is a tree."<<endl;        else            cout<<"is not a tree."<<endl;        cc++;    }    return 0;}