无向图最大匹配

//hdu 4687

int pre[N];
int match[N];
int fa[N];
int Find(int u){
    if(u==fa[u])return u;
    return fa[u]=Find(fa[u]);
}
void Union(int u,int v){
    u=Find(u),v=Find(v);
    if(u!=v)fa[u]=v;
}
vector<int> E[N];
int Q[N],bot;
int mark[N];
int vis[N];
int ti;
int lca(int x,int y){
    ti++;
    while(1){
        if(x!=-1){
            x=Find(x);
            if(vis[x]==ti)return x;
            vis[x]=ti;
            if(match[x]!=-1)x=pre[match[x]];
            else x=-1;
        }
        swap(x,y);
    }
}
void goup(int a,int p){
    while(a!=p){
        int b=match[a],c=pre[b];
        if(Find(c)!=p)pre[c]=b;
        if(mark[b]==2)mark[Q[bot++]=b]=1;
        if(mark[c]==2)mark[Q[bot++]=c]=1;
        Union(a,b);
        Union(b,c);
        a=c;
    }
}
void augment(int s){
    Q[0]=s;bot=1;mark[s]=1;
    for(int head=0;match[s]==-1&&head<bot;head++){
        int x=Q[head];
        for(int i=0;i<E[x].size();i++){
            int y=E[x][i];
            if(match[x]!=y&&Find(x)!=Find(y)&&mark[y]!=2){
                if(mark[y]==1){
                    int p=lca(x,y);
                    if(Find(x)!=p)pre[x]=y;
                    if(Find(y)!=p)pre[y]=x;
                    goup(x,p);
                    goup(y,p);
                }
                else if(match[y]==-1){
                    pre[y]=x;
                    int j=y;
                    while(j!=-1){
                        int k=pre[j];
                        int l=match[k];
                        match[j]=k;match[k]=j;
                        j=l;
                    }
                    break;
                }
                else {
                    pre[y]=x;
                    mark[Q[bot++]=match[y]]=1;
                    mark[y]=2;
                }
            }
        }
    }
}

int _hu(int n){
    int ans=0;
    for (int i=0;i<n;i++)match[i]=-1;
    for (int i=0;i<n;i++)if(match[i]==-1){
        ti=0;
        for(int j=0;j<n;j++){
            pre[j]=-1,fa[j]=j,mark[j]=0,vis[j]=-1;
        }
        augment(i);
    }
    for(int i=0; i<n; ++i)
        E[i].clear();
    for(int i=0;i<n;i++)if(match[i]!=-1){
        ans++;
    }
    return ans/2;
}