hdu 4115 Eliminate the Conflict

2sat题目，正确理解2sat即可。

#include <iostream>
#include <cstdio>
#include <cstring>
using namespace std;
const int maxn=(1e4+9)*2;
int n,m;
int a[maxn][2];

int dfn[maxn],low[maxn],stack[maxn],instack[maxn],s[maxn],un[maxn];
int count,top,con;


int head[maxn<<1],lon;
struct
{
    int next,to;
}e[maxn*100];

void edgeini()
{
    memset(head,-1,sizeof(head));
    lon=-1;
}
void edgemake(int from,int to)
{
    e[++lon].to=to;
    e[lon].next=head[from];
    head[from]=lon;
}

void make(int from,int tmp,int to)
{
    if(a[from][tmp]==a[to][0])
    edgemake(from*2-tmp,to*2);
    else if(a[from][tmp]==a[to][1])
    edgemake(from*2-tmp,to*2-1);
    else edgemake(from*2-tmp,from*2-(tmp^1));
}

void built(int from,int tmp,int to)
{
    if(a[from][tmp]==a[to][0])
    edgemake(from*2-tmp,to*2-1);
    else if(a[from][tmp]==a[to][1])
    edgemake(from*2-tmp,to*2);
}

void tarjan(int t)
{
    dfn[t]=low[t]=++count;
    instack[t]=1;
    stack[++top]=t;
    for(int k=head[t];k!=-1;k=e[k].next)
    {
        int u=e[k].to;
        if(dfn[u]==-1)
        {
            tarjan(u);
            low[t]=min(low[t],low[u]);
        }
        else if(instack[u])
        low[t]=min(low[t],dfn[u]);
    }
    if(dfn[t]==low[t])
    {
        ++con;
        while(1)
        {
            int u=stack[top--];
            instack[u]=0;
            s[u]=con;
            if(u==t) break;
        }
    }
}


void tarjan()
{
    memset(dfn,-1,sizeof(dfn));
    memset(instack,0,sizeof(instack));
    count=top=con=0;
    for(int i=1;i<=n+n;i++)
    if(dfn[i]==-1)
    tarjan(i);
}

bool chk()
{
    for(int i=1;i<=n+n;i+=2)
    if(s[i]==s[i+1])
    return false;
    return true;
}

void solve()
{
    tarjan();
    bool ans=chk();
    if(ans) printf("yes\n");
    else printf("no\n");
}


int main()
{
//    freopen("in.txt","r",stdin);
    int T,cas=0;
    scanf("%d",&T);
    while(T--)
    {
        edgeini();
        scanf("%d%d",&n,&m);
        for(int i=1;i<=n;i++)
        {
            scanf("%d",&a[i][0]);
            if(a[i][0]==3) a[i][1]=1;
            else a[i][1]=a[i][0]+1;
        }
        for(int k=1,from,to,w;k<=m;k++)
        {
            scanf("%d%d%d",&from,&to,&w);
            if(w==0)
            {
                make(from,0,to);
                make(from,1,to);
                make(to,0,from);
                make(to,1,from);
            }
            else
            {
                built(from,0,to);
                built(from,1,to);
                built(to,0,from);
                built(to,1,from);
            }
        }
        printf("Case #%d: ",++cas);
        solve();
    }
    return 0;
}