poj 3678 2-sat 建图非常容易错！！

改天把2-sat刷完了再一起总结吧，先放这儿

#include<stdio.h>
#include<string.h>
#include<vector>
#include<algorithm>
using namespace std;
const int MAX =20010;
vector<int> edge[MAX];
int st[MAX];
int dfn[MAX],low[MAX];
int top,btype,tdfn;
int belong[MAX];
bool ins[MAX];
void dfs(int s)
{
	int i,t;
	dfn[s]=low[s]=++tdfn;
	ins[s]=true;
	st[++top]=s;
	for(i=0;i<edge[s].size();i++)
	{
		t=edge[s][i];
		if(!dfn[t])
		{
			dfs(t);
			if(low[t]<low[s]) low[s]=low[t];
		}
		else if(ins[t] && dfn[t]<low[s])  low[s]=dfn[t];
	}
	if(dfn[s]==low[s])
	{
		btype++;
		do
		{
			t=st[top--];
			ins[t]=false;
			belong[t]=btype;
		}while(t!=s);
	}
}
void SCC(int n)
{
	int i;
	top=btype=tdfn=0;
	memset(ins,false,sizeof(ins));
	memset(dfn,0,sizeof(dfn));
	for(i=1;i<=n;i++)
		if(!dfn[i])
			dfs(i);
}
int main()
{
    int i,j,k;
	int n,m;
	int a,b,c;
	scanf("%d%d",&n,&m);
	char str[5];
	for(i=0;i<m;i++)
	{
		scanf("%d%d%d%s",&a,&b,&c,str);
		a++,b++;
		if(strcmp(str,"AND")==0)
		{
			if(c==0)
			{
				edge[b+n].push_back(a);
				edge[a+n].push_back(b);
			}
			else 
			{
				edge[a+n].push_back(b+n);
				edge[b+n].push_back(a+n);
				edge[a].push_back(a+n);
				edge[b].push_back(b+n);
			}
		}
		else if(strcmp(str,"OR")==0)
		{
			if(c==0)
			{
				edge[a].push_back(b);
				edge[b].push_back(a);
				edge[a+n].push_back(a);
				edge[b+n].push_back(b);
			}
			else 
			{
				edge[a].push_back(b+n);
				edge[b].push_back(a+n);
			}
		}
		else 
		{
			if(c==0)
			{
				edge[a].push_back(b);
				edge[b].push_back(a);
				edge[a+n].push_back(b+n);
				edge[b+n].push_back(a+n);
			}
			else 
			{
				edge[a].push_back(b+n);
				edge[b].push_back(a+n);
				edge[a+n].push_back(b);
				edge[b+n].push_back(a);
			}
		}
	}
	SCC(2*n);
	int flag=1;
	for(i=1;i<=n;i++)
	{
		if(belong[i]==belong[i+n])
		{
			flag=0;
			break;
		}
	}
	if(flag==0) printf("NO\n");
	else printf("YES\n");
	return 0;
}