hdu 1325 Is It A Tree? 判断是一棵树还是有回路

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.

#include<iostream>
 #include<stdlib.h>
 #include<stdio.h>
 #include<cstring>
 #include<string>
 #include<stack>

 using namespace std;
 int root[1000],leaf[1000];

 int main()
 {
 int a,b,t=1,flag=1,max=0,flag2=0;//flag2主要用来判断是不是一颗空树，空树也是树


 while(cin>>a>>b)
 {
 if(a==-1) break;


 if(a==0&&b==0)
 {
 if(flag2==1&&flag==1){
 int sum=0;
 for(int i=1;i<1000;i++)
 {
 if(root[i]>0&&leaf[i]==0) sum++;//只能有一个树根
 }

 if(sum!=1) flag=0;
 }

 memset(root,0,sizeof(root));
 memset(leaf,0,sizeof(leaf));
 if(flag) cout<<"Case "<<t<<" is a tree."<<endl;
 else  cout<<"Case "<<t<<" is not a tree."<<endl;
 t++;
 flag=1;
 flag2=0;
 max=0;

 continue;
 }
 flag2=1;

 root[a]++;//表示a的叶子个数
 leaf[b]++;//b的根个数
 if(leaf[b]>1) flag=0;//如果有一个叶子有多个根 则形成回路，不符合要求



 }
 }

转载于:https://www.cnblogs.com/LandingGuy/p/9280296.html