HDU3062 Party (2-SAT)

没注意边数T了N遍的我真是弱啊

const int N = 2007;

int n;

struct Edge{
	int nxt,pre;
}e[1000007];
int cntEdge,head[N];
inline void add(int u,int v){
	e[++cntEdge] = (Edge){head[u], v}, head[u] = cntEdge;
}

int dfn[N],dfnIndex,low[N],vis[N];
int sta[N],top;
int bcc[N],bccIndex;
inline void Tarjan(int u){
	dfn[u] = low[u] = ++dfnIndex;
	vis[u] = true;
	sta[++top] = u;
	for(register int i = head[u]; i; i = e[i].nxt){
		int v = e[i].pre;
		if(!dfn[v]){
			Tarjan(v);
			low[u] = Min(low[u], low[v]);
		}
		else if(vis[v]){
			low[u] = Min(low[u], dfn[v]);
		}
	}
	if(dfn[u] == low[u]){
		++bccIndex;
		do{
			bcc[sta[top]] = bccIndex;
			vis[sta[top]] = false;
		}while(sta[top--] != u);
	}
	
}

inline bool Judge(){
	R(i,1,n){
		if(bcc[i<<1] == bcc[i<<1|1])
			return false;
	}
	return true;
}
int main(){
	int m;
	while(~scanf("%d%d", &n, &m)){
		cntEdge = 0;
		n <<= 1;
		R(i,1,n){
			head[i] = 0,
			dfn[i] = 0,
			low[i] = 0,
			vis[i] = false;
		}
		n >>= 1;

		R(i,1,m){
			int a,b,c,d;
			io >> a >> b >> c >> d;
			a = (a<<1) + c;
			b = (b<<1) + d;
			add(a, b ^ 1);
			add(b, a ^ 1);
		}
		
		n <<= 1;
		R(i,1,n){
			if(!dfn[i])
				Tarjan(i);
		}
		n >>= 1;
		
		if(Judge() == true)
			printf("YES
");
		else
			printf("NO
");
	}
	return 0;
}