2-sat模版（转自acm再见）

//2-sat模版
const int maxn=10005*3;
int n,m;
int a[maxn],b[maxn];
struct note
{
    int to;
    int nxt;
}edge[maxn*2];
int head[maxn];
int ip;
int dfn[maxn],low[maxn],sccno[maxn],cnt,scc,instack[maxn];
stack<int> stk;
void init()
{
    memset(head,-1,sizeof(head));
    ip=1;
}
void addedge(int u,int v)
{
    edge[ip].to=v,edge[ip].nxt=head[u],head[u]=ip++;
}
// x = xval or y = yval
//void add_cluse(int x,int xval,int y,int yval)
//{
//    x=x*2+xval;
//    y=y*2+yval;
//    addedge(x,y^1);
//    addedge(y,x^1);
//}
void dfs(int u)
{
    dfn[u]=low[u]=++scc;
    stk.push(u);
    instack[u]=1;
    for (int i=head[u]; i!=-1; i=edge[i].nxt)
    {
        int v=edge[i].to;
        if (!dfn[v])
        {
            dfs(v);
            low[u]=min(low[u],low[v]);
        }
        else if (instack[v])
            low[u]=min(low[u],dfn[v]);
    }
    if (low[u]==dfn[u])
    {
        cnt++;
        int x;
        do
        {
            x=stk.top();
            stk.pop();
            sccno[x]=cnt;
            instack[x]=0;
        }while (x!=u);
    }
}
bool solve()
{
    scc=cnt=0;
    memset(sccno,0,sizeof(sccno));
    memset(dfn,0,sizeof(dfn));
    memset(low,0,sizeof(low));
    memset(instack,0,sizeof(instack));
    while (!stk.empty()) stk.pop();
    for (int i=0; i<2*n; i++) if (!dfn[i]) dfs(i);
    for (int i=0; i<2*n; i+=2)
    {
        if (sccno[i]==sccno[i^1]) return false;
    }
    return true;
}