NOIP 考前 并查集复习

POJ 1182

把一个点拆成x,x+n,x+2*n，x吃y可以表示认为x，y+n是一类的，x+n，y+2*n是一类，x+2*n,y是一类。

#include <cstdio>

const int Maxn=50100;
int F[Maxn*3],n,k,Type,x,y,Ans;
int Get(int x) {return F[x]==x?x:F[x]=Get(F[x]);}
int main()
{
    scanf("%d%d",&n,&k);
    for (int i=1;i<=3*n;i++) F[i]=i;
    for (int i=1;i<=k;i++)
    {
        scanf("%d%d%d",&Type,&x,&y);
        if (x>n || y>n || (x==y && Type==2))
        {
            Ans++;
            continue;
        }
        
        if (Type==1)
        {
            if (Get(x)==Get(y+n) || Get(x)==Get(y+2*n))
            {
                Ans++;
                continue;
            }
            F[Get(x)]=Get(y);
            F[Get(x+n)]=Get(y+n);
            F[Get(x+2*n)]=Get(y+2*n);
        } else 
        {
            if (Get(x)==Get(y) || Get(x)==Get(y+2*n))
            {
                Ans++;
                continue;
            }
            F[Get(x)]=Get(y+n);
            F[Get(x+n)]=Get(y+2*n);
            F[Get(x+2*n)]=Get(y);
        }
    }
    printf("%d
",Ans);
    return 0;
}

HDU 3047

Sum[x]表示fa[x]和x的差. 带权并查集

#include <cstdio>

int Sum[50010],Father[50010],n,m,Count,u,v,w;
int Get_Father(int x)
{
    if (x==Father[x]) return x;
    int Tmp=Get_Father(Father[x]);
    Sum[x]+=Sum[Father[x]];
    return Father[x]=Tmp;
}
int main()
{
    while (scanf("%d%d",&n,&m)!=EOF)
    {
        for (int i=0;i<=n;i++) Father[i]=i,Sum[i]=0;
        Count=0;
        for (int i=1;i<=m;i++)
        {
            scanf("%d%d%d",&u,&v,&w);
            int fu=Get_Father(u),fv=Get_Father(v);
            if (fu!=fv) 
            {
                Father[fu]=fv;
                Sum[fu]=Sum[v]+w-Sum[u];
            } else 
            {
                if (Sum[u]-Sum[v]!=w)
                    Count++;
            }
        }
        printf("%d
",Count);
    }
    return 0;
}

BZOJ 1202

带权并查集

#include <cstdio>
int KASE,n,m,u,v,w;
int Father[20010],Sum[20010]; 
int Get_Father(int x)
{
    if (x==Father[x]) return x;
    int Tmp=Get_Father(Father[x]);
    Sum[x]+=Sum[Father[x]];
    Father[x]=Tmp;
    return Tmp;
}
int main()
{
    scanf("%d",&KASE);
    for (int Kase=1;Kase<=KASE;Kase++)
    {
        scanf("%d%d",&n,&m); bool flag=false;
        for (int i=0;i<=n;i++) Father[i]=i,Sum[i]=0;
        for (int i=1;i<=m;i++)
        {
            scanf("%d%d%d",&u,&v,&w);
            int fu=Get_Father(u-1),fv=Get_Father(v);
            if (fu==fv)
            {
                if (Sum[u-1]-Sum[v]!=w) 
                {
                    flag=true;
                    break;
                }
            } else
            {
                Father[fu]=fv;
                Sum[fu]=Sum[v]-Sum[u-1]+w;
            }
        }
        puts(flag?"false":"true");
    }
    return 0;
}