浙大校赛 I 用了并查集

浙大校赛 I 用了并查集

题意严重不明，开始还以为是顶点按顺序形成环，WA了N次之后改了算法才过的。。。

#include < iostream >
#include < algorithm >
#include < cstdio >
using   namespace  std;


int  n,m;
int  v[ 100 ][ 100 ];
int  d[ 100 ];

int  f[ 1000 ];
int  r[ 1000 ];
int  find( int  n)
{
    if(f[n]==n)
        return n;
    else
        f[n]=find(f[n]);
    return f[n];
}


int  Union( int  x, int  y)
{
    int a=find(x);
    int b=find(y);
    if(a==b)
        return 0;
    else if(r[a]<=r[b])
    {
        f[a]=b;
        r[b]+=r[a];
    }
    else
    {
        f[b]=a;
        r[a]+=r[b];
    }
    return 1;

}

int  main()
{

    while(scanf("%d%d",&n,&m)!=EOF)
    {

        int flag=0;
        memset(d,0,sizeof(d));
        int i,j;
        for(i=0;i<n;i++)
        {

            f[i]=i;
            r[i]=1;
        }
        for(i=1;i<=m;i++)
        {
            int a,b;
            scanf("%d%d",&a,&b);
            Union(a,b);
            d[a]++;
            d[b]++;
        }
        int tt=find(1);
        if(r[tt]!=n)
        {

            printf("NO\n");
            continue;
        }

        if(n!=m||n<3)
        {
            printf("NO\n");
            continue;
        }
        for(i=1;i<=n;i++)
        {

            if(d[i]!=2)
            {
                flag=1;
                break;
            }
        }
        if(flag)
            printf("NO\n");
        else
            printf("YES\n");

    }
    return 0;
}