2-SAT模板

#include <iostream>#include <cstdio>#include <cstring>using namespace std;const int maxn=4444;const int maxm=1111111;struct EDGE{    int to;    int w;    int next;}edges[maxm];int head[maxn];int edge,node;int lowlink[maxn],pre[maxn],sccno[maxn],stk[maxn],top,dfs_clock,scc_cnt;void prepare(int _node){    node=_node;    for (int i=0;i<=node;i++) head[i]=-1;    edge=0;}void addedge(int u,int v,int c=1){    edges[edge].w=c,edges[edge].to=v,edges[edge].next=head[u],head[u]=edge++;}void Tarjan_dfs(int u){    int i,v;    pre[u]=lowlink[u]=++dfs_clock;    stk[top++]=u;    for(i=head[u];i!=-1;i=edges[i].next)        if(!pre[v=edges[i].to])            Tarjan_dfs(v),lowlink[u]=min(lowlink[u],lowlink[v]);        else if(!sccno[v])            lowlink[u]=min(lowlink[u],pre[v]);    if(pre[u]==lowlink[u])    {        sccno[u]=++scc_cnt;        while(stk[--top]!=u)sccno[stk[top]]=scc_cnt;    }}void Tarjan_find_scc(){    int i;    scc_cnt=dfs_clock=top=0;    memset(sccno,0,sizeof(sccno));    memset(pre,0,sizeof(pre));    for(i=0;i<node;i++)        if(!pre[i]) Tarjan_dfs(i);}bool two_sat(){    for(int i=0;i<node;i+=2)        if(sccno[i]==sccno[i^1])return false;    return true;}