poj 1308 Is It A Tree?(并查集)

来源：互联网发布：python读取dat文件编辑：程序博客网时间：2024/06/14 09:43

思路同hdu 1272

#include<iostream>#include<stdio.h>#include<string.h>using namespace std;#define MAXN 1005int fa[MAXN],sign[MAXN],flag;int set_find(int d){    if(fa[d]<0)return d;    return fa[d]=set_find(fa[d]);}void set_join(int x,int y){    x=set_find(x);    y=set_find(y);    if(x!=y)fa[x]=y;    else flag=0;//同一个父节点，成环}int main(){    int i,a,b,cas=1;    while(cin>>a>>b)    {        if(a==-1&&b==-1) break;        if(a==0&&b==0)        {            cout<<"Case "<<cas++<<" is a tree."<<endl;            continue;        }        for(i=1; i<MAXN; i++)        {            fa[i]=-1;            sign[i]=0;        }        sign[a]=sign[b]=1;        flag=1;        set_join(a,b);        while(cin>>a>>b)        {            if(a==0&&b==0) break;            set_join(a,b);            sign[a]=sign[b]=1;        }        int k=0;        for(i=1; i<MAXN; i++)        {            if(sign[i]&&fa[i]==-1) //判断根节点k数目                k++;            if(k>1) flag=0;        }        if(flag) cout<<"Case "<<cas++<<" is a tree."<<endl;        else cout<<"Case "<<cas++<<" is not a tree."<<endl;    }    return 0;}

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