思路:裸的2-SAT。
#include<map>
#include<set>
#include<cmath>
#include<queue>
#include<cstdio>
#include<vector>
#include<string>
#include<cstdlib>
#include<cstring>
#include<iostream>
#include<algorithm>
#define Maxn 2010
#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 dfn[Maxn],low[Maxn],id[Maxn],Stack[Maxn],lab,num,e,top,vi[Maxn],n,m;
vector<int> head[Maxn];
void init()
{
memset(dfn,,sizeof(dfn));
memset(low,,sizeof(low));
lab=num=top=;
memset(vi,,sizeof(vi));
memset(id,,sizeof(id));
for(int i=;i<=*n;i++)
head[i].clear();
}
void Tarjan(int u)
{
int i,v,sz;
dfn[u]=low[u]=++lab;
Stack[top++]=u;
vi[u]=;
sz=head[u].size();
for(i=;i<sz;i++){
v=head[u][i];
if(!dfn[v]){
Tarjan(v);
low[u]=min(low[v],low[u]);
}
if(vi[v])
low[u]=min(low[u],dfn[v]);
}
if(low[u]==dfn[u]){
++num;
do{
i=Stack[--top];
id[i]=num;
vi[i]=;
}while(i!=u);
}
return ;
}
int main()
{
int i,j,a,b,c,d;
while(scanf("%d",&n)!=EOF){
init();
scanf("%d",&m);
for(i=;i<=m;i++){
scanf("%d%d%d%d",&a,&b,&c,&d);
a++;
b++;
if(c==&&d==)
head[a].push_back(b+n),head[b].push_back(a+n);
if(c==&&d==)
head[a].push_back(b),head[b+n].push_back(a+n);
if(c==&&d==)
head[a+n].push_back(b+n),head[b].push_back(a);
if(c==&&d==)
head[a+n].push_back(b),head[b+n].push_back(a);
}
for(i=;i<=*n;i++){
if(!dfn[i])
Tarjan(i);
}
for(i=;i<=n;i++)
if(id[i]==id[i+n])
break;
if(i<=n)
printf("NO\n");
else
printf("YES\n");
}
return ;
}