hdu 3234 并查集

虚拟一个根节点n,设其值为0.并且始终保持其为根。

#include<map>

#include<set>

#include<cmath>

#include<queue>

#include<cstdio>

#include<vector>

#include<string>

#include<cstdlib>

#include<cstring>

#include<iostream>

#include<algorithm>

#define Maxn 40010

#define Maxm 100010

#define LL __int64

#define Abs(x) ((x)>0?(x):(-x))

#define lson(x) (x<<1)

#define rson(x) (x<<1|1)

#define inf 0x7fffffff

#define Mod 1000000007

using namespace std;

int fa[Maxn],val[Maxn],n;

map<int,int> num;

void init()

{

    for(int i=0;i<Maxn;i++){

        fa[i]=i;

        val[i]=0;

    }

}

int find(int x)

{

    if(fa[x] == x)

    return x;

    int t = find(fa[x]);

    val[x] ^= val[fa[x]];

    fa[x] = t;

    return t;

}

int merg(int a,int b,int v)

{

    int x=find(a);

    int y=find(b);

    if(x==y){

        return (val[a]^val[b])==v;

    } //cout<<x<<" * "<<y<<endl;

    if(x==n){

        fa[y]=x;

        val[y]=val[a]^val[b]^v;

        return 1;

    }

    if(y==n){

        fa[x]=y;

        val[x]=val[a]^val[b]^v;

        return 1;

    }

    fa[x]=y;

    val[x]=val[a]^val[b]^v;

    return 1;

}

int main()

{

    int q,i,j,x,y,v,cnt=0,k,ans,ok,Case=0;

    char str[20],ch[5];

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

        init();

        int err=0;

        cnt=0;

        printf("Case %d:\n",++Case);

        for(i=1;i<=q;i++){

            scanf("%s",ch);

            if(ch[0]=='I'){

                gets(str);

                if(err) continue;

                ++cnt;

                if(sscanf(str,"%d %d %d",&x,&y,&v)==2){

                    v=y;

                    y=n;

                    //cout<<x<<" "<<y<<" "<<v<<endl;

                    if(!merg(x,y,v)){

                        err=1,printf("The first %d facts are conflicting.\n",cnt);

                    }

                }

                else {

                    //cout<<x<<" "<<y<<" "<<v<<endl;

                    if(!merg(x,y,v)){

                        err=1,printf("The first %d facts are conflicting.\n",cnt);

                    }

                }

            }

            else {

                scanf("%d",&k);

                ans=0;

                ok=0;

                num.clear();

                for(j=1;j<=k;j++){

                    scanf("%d",&x);

                    if(err) continue;

                    int t=find(x);

                    ans^=val[x];

                    //cout<<t<<" "<<x<<" "<<find(0)<<endl;

                    if(t!=n){

                        if(num[t]%2==0){

                            ok++;

                            num[t]++;

                        }else ok--,num[t]--;

                    }

                }

                if(err) continue;

                if(!ok){

                    printf("%d\n",ans);

                }else{

                    printf("I don't know.\n");

                }

            }

        }

        printf("\n");

    }

    return 0;

}