Luogu4782 【模板】2-SAT 问题（2-SAT）

　　模板。注意若x=y不一定是废话，x=0或x=0表示x必须为0。以及数组开2n。

#include<iostream>
#include<cstdio>
#include<cmath>
#include<cstdlib>
#include<cstring>
#include<algorithm>
using namespace std;
int read()
{
    int x=,f=;char c=getchar();
    while (c<''||c>'') {if (c=='-') f=-;c=getchar();}
    while (c>=''&&c<='') x=(x<<)+(x<<)+(c^),c=getchar();
    return x*f;
}
#define N 2000010
int n,m,p[N],t=;
int dfn[N],low[N],stk[N],set[N],top=,cnt=;
bool flag[N];
struct data{int to,nxt;
}edge[N];
void addedge(int x,int y){t++;edge[t].to=y,edge[t].nxt=p[x],p[x]=t;}
void tarjan(int k)
{
    dfn[k]=low[k]=++cnt;
    stk[++top]=k;flag[k]=;
    for (int i=p[k];i;i=edge[i].nxt)
    if (!dfn[edge[i].to]) tarjan(edge[i].to),low[k]=min(low[k],low[edge[i].to]);
    else if (flag[edge[i].to]) low[k]=min(low[k],dfn[edge[i].to]);
    if (dfn[k]==low[k])
    {
        t++;
        while (stk[top]!=k)
        {
            set[stk[top]]=t;
            flag[stk[top]]=;
            top--;
        }
        set[k]=t;flag[k]=;top--;
    }
}
int main()
{
#ifndef ONLINE_JUDGE
    freopen("2-SAT.in","r",stdin);
    freopen("2-SAT.out","w",stdout);
    const char LL[]="%I64d";
#else
    const char LL[]="%lld";
#endif
    n=read(),m=read();
    for (int i=;i<=m;i++)
    {
        int x=read(),w=read(),y=read(),v=read();
        if (x!=y) addedge(x*-(w^),y*-v),addedge(y*-(v^),x*-w);
        else if (w==v) addedge(x*-(w^),x*-w);
    }
    t=;
    for (int i=;i<=n*;i++)
    if (!dfn[i]) tarjan(i);
    for (int i=;i<=n;i++)
    if (set[i<<]==set[i*-]) {cout<<"IMPOSSIBLE";return ;}
    cout<<"POSSIBLE\n";
    for (int i=;i<=n;i++)
    if (set[i<<]<set[i*-]) printf("0 ");else printf("1 ");
    return ;
}