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;

}