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;
}