2-SAT（luoguP4782）

題目鏈接：https://www.luogu.org/problemnew/show/P4782

思路：模板題，這類題感覺主要還是寫出布爾表達式比較重要

#include <cstdio>
#include <cstdlib>
#include <cassert>
#include <cstring>
#include <bitset>
#include <cmath>
#include <cctype>
#include <iostream>
#include <algorithm>
#include <string>
#include <vector>
#include <queue>
#include <stack>
#include <map>
#include <set>
#include <sstream>
#include <iomanip>
using namespace std;
typedef long long ll;
typedef vector<long long> VI;
typedef unsigned long long ull;
const ll inff = 0x3f3f3f3f3f3f3f3f;
#define FOR(i,a,b) for(int i(a);i<=(b);++i)
#define FOL(i,a,b) for(int i(a);i>=(b);--i)
#define SZ(x) ((long long)(x).size())
#define REW(a,b) memset(a,b,sizeof(a))
#define inf int(0x3f3f3f3f)
#define si(a) scanf("%d",&a)
#define sl(a) scanf("%lld",&a)
#define sd(a) scanf("%lf",&a)
#define ss(a) scanf("%s",a)
#define mod ll(1e9+7)
#define pb push_back
#define eps 1e-6
#define lc d<<1
#define rc d<<1|1
#define Pll pair<ll,ll>
#define P pair<int,int>
#define pi acos(-1)
int n,dfn[2000008],vis[2000008],low[2000008],z[2000008],m,x,y,q,w,deep,sum,tmp;
vector<int>g[2000008];
stack<int>st;
void tarjan(int u)
{
    dfn[u]=low[u]=++deep;
    vis[u]=1,st.push(u);
    for(int i=0;i<g[u].size();i++)
    {
        int v=g[u][i];
        if(!dfn[v])
        {
            tarjan(v);
            low[u]=min(low[u],low[v]);
        }
        else if(vis[v])  low[u]=min(low[u],dfn[v]);
    }
    if(dfn[u]==low[u])
    {
        sum++,tmp=0;
        while(tmp!=u)
        {
            tmp=st.top();st.pop();
            z[tmp]=sum;
            vis[tmp]=0;
        }
    }
}
int main()
{
    cin.tie(0);
    cout.tie(0);
    cin>>n>>m;
    while(m--)
    {
        si(x),si(q),si(y),si(w);
        g[x+n*(q&1)].pb(y+n*(w^1));
        g[y+n*(w&1)].pb(x+n*(q^1));
    }
    FOR(i,1,2*n) if(!dfn[i]) tarjan(i);
    FOR(i,1,n) if(z[i]==z[i+n]) return puts("IMPOSSIBLE"),0;
    puts("POSSIBLE");
    FOR(i,1,n) printf("%d ",(z[i]<z[i+n]));
    puts("");
    return 0;
}