SPOJ IM_Intergalactic Map

#include <iostream>
#include <cstdio>
#include <cstring>
#include <map>
#define maxn 2001000
#define maxm 5002000
using namespace std;

int L[maxn],R[maxn],Li[maxn],Ri[maxn];
int to[maxm],next[maxm],c[maxm],first[maxn],edge,node;
int from[maxn],tag[maxn],TAG=520;
int Q[maxm],bot,top;
int n,m,s,t,T;

int addnode()
{
    first[++node]=-1;
    return node;
}

void addedge(int U,int V)
{
    edge++;
    to[edge]=V,c[edge]=1,next[edge]=first[U],first[U]=edge;
    edge++;
    to[edge]=U,c[edge]=0,next[edge]=first[V],first[V]=edge;
}

void _input()
{
    int U,V;
    node=0,edge=-1;
    scanf("%d%d",&n,&m);
    while (m--)
    {
        scanf("%d%d",&U,&V);
        if (Li[U]!=TAG) Li[U]=TAG,L[U]=addnode(),R[U]=addnode(),addedge(L[U],R[U]);
        if (Li[V]!=TAG) Li[V]=TAG,L[V]=addnode(),R[V]=addnode(),addedge(L[V],R[V]);
        addedge(R[U],L[V]),addedge(R[V],L[U]);
    }
    t=addnode();
    if (Li[2]==TAG) s=R[2];
        else s=addnode();
    if (Li[1]==TAG) addedge(R[1],t);
    if (Li[3]==TAG) addedge(R[3],t);
}

bool EK()
{
    Q[bot=top=1]=s,tag[s]=++TAG,from[s]=-1;
    while (bot<=top)
    {
        int cur=Q[bot++];
        for (int i=first[cur]; i!=-1; i=next[i])
            if (c[i]>0 && tag[to[i]]!=TAG)
            {
                Q[++top]=to[i],from[to[i]]=i,tag[to[i]]=TAG;
                if (to[i]==t)
                {
                    for (int k=t; from[k]!=-1; k=to[from[k]^1])
                        c[from[k]]--,c[from[k]^1]++;
                    return true;
                }
            }
    }
    return false;
}

int main()
{
    scanf("%d",&T);
    while (T--)
    {
        _input();
        if (EK() && EK()) puts("YES");
            else puts("NO");
    }
    return 0;
}