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;}