Graph Theory NO.3 HDU_1325_Is It A Tree_并查集

#include <cstdio>#include <cstring>#include <algorithm>#include <iostream>using namespace std;#define M 100009int k=1;int father[M];int d[M];//入度int mark[M];void Init(int n)//初始化{    for(int i=1;i<=n;i++)    {        father[i]=i;    }}int Find(int n)//查找根{    if(n!=father[n])    {        father[n]=Find(father[n]);    }    return father[n];}int Union(int n,int m){    if(n==m)        return 0;    else    {        father[n]=m;    }    return 0;}int main(){    int a,b;    memset(d,0,sizeof(d));    int num=0;    int flag=0;    Init(M);    int count=0;    memset(mark,0,sizeof(mark));    while(~scanf("%d%d",&a,&b))    {        if(a<0&&b<0)            break;        if(a!=0&&b!=0)        {            mark[num++]=a;            mark[num++]=b;            if(father[a]==father[b])            {                flag=1;                //printf("*1\n");            }            Union(Find(a),Find(b));            d[b]++;        }        else        {            for(int i=0;i<num;i++)            {                if(d[mark[i]]>1)                {                    flag=1;                    //printf("*2\n");                }                if(father[mark[i]]==mark[i])                {                    count++;                    //printf("*3\n");                }            }            if(count>1)            {                flag=1;                //printf("*4\n");            }            if(flag==0)            {                printf("Case %d is a tree.\n",k++);            }            else            {                printf("Case %d is not a tree.\n",k++);            }            memset(d,0,sizeof(d));            memset(mark,0,sizeof(mark));            num=0;            flag=0;            Init(M);            count=0;        }    }    return 0;}/*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*/