luogu 4782【模板】 2-SAT 问题

2-SAT就是给出$m$个限制表示$x==val_x || y==val_y$

求出满足的解

每个点拆成两个点，如果$x$不满足则$y$一定满足，$y$不满足同理。这样我们连边，然后$tarjan$即可

 #include<iostream>
 #include<cstdio>
 #include<cstring>
 #include<cstdlib>
 #include<cmath>
 #include<algorithm>
 #include<queue>
 #include<vector>
 #include<map>
 #include<set>
 #define ll long long
 #define db double
 #define inf 2139062143
 #define MAXN 2001000
 #define rep(i,s,t) for(register int i=(s),i##__end=(t);i<=i##__end;++i)
 #define dwn(i,s,t) for(register int i=(s),i##__end=(t);i>=i##__end;--i)
 #define ren for(register int i=fst[x];i;i=nxt[i])
 #define pb(i,x) vec[i].push_back(x)
 #define pls(a,b) (a+b)%MOD
 #define mns(a,b) (a-b+MOD)%MOD
 #define mul(a,b) (1LL*(a)*(b))%MOD
 using namespace std;
 inline int read()
 {
     int x=,f=;char ch=getchar();
     while(!isdigit(ch)) {if(ch=='-') f=-;ch=getchar();}
     while(isdigit(ch)) {x=x*+ch-'';ch=getchar();}
     return x*f;
 }
 int n,m,nxt[MAXN<<],fst[MAXN],to[MAXN<<],cnt;
 int dfn[MAXN],low[MAXN],bl[MAXN],stp,st[MAXN],top,scc;
 void add(int u,int v) {nxt[++cnt]=fst[u],fst[u]=cnt,to[cnt]=v;}
 void tarjan(int x)
 {
     st[++top]=x,dfn[x]=low[x]=++stp;
     ren if(!dfn[to[i]]) {tarjan(to[i]);low[x]=min(low[x],low[to[i]]);}
         else if(!bl[to[i]]) low[x]=min(low[x],dfn[to[i]]);
     if(low[x]==dfn[x])
         {scc++;int now=;while(now!=x) now=st[top--],bl[now]=scc;}
 }
 int main()
 {
     n=read(),m=read();int a,b,x,y;rep(i,,m)
         a=read(),x=read(),b=read(),y=read(),
         add(a+(^x)*n,b+y*n),add(b+(^y)*n,a+x*n);
     rep(i,,n<<) if(!dfn[i]) tarjan(i);
     rep(i,,n) if(bl[i]==bl[i+n]) return puts("IMPOSSIBLE"),;puts("POSSIBLE");
     rep(i,,n) printf("%d ",bl[i]>bl[i+n]);
 }