洛谷P-4782 2-sat+Tarjan

https://www.luogu.org/problemnew/solution/P4782

这里的大佬已经说的够好了

#include<iostream>
#include<cstring>
#include<cstdio>
#include<algorithm>
#include<vector>
#include<stack>
#define maxn 2002010
using namespace std;
vector<int>G[maxn];
stack<int>s;
void insert(int be, int en) {
	G[be].push_back(en);
}
int low[maxn], dfn[maxn], df, ans, clor[maxn];
int tarjan(int x) {
	//cout << x << endl;
	low[x] = dfn[x] = ++df;
	s.push(x);
	for (int i = 0; i < G[x].size(); i++) {
		int p = G[x][i];
 
		if (!dfn[p]) {
			tarjan(p);
			low[x] = min(low[x], low[p]);
		}
		else if (!clor[p]) {
			low[x] = min(low[x], dfn[p]);
		}
	}
	if (low[x] == dfn[x]) {
		ans++;
		while (1) {
			int a = s.top();
			s.pop();
			clor[a] = ans;
			if (a == x) break;
		}
	}
	return 0;
}
int n, m;
 
int main() {
	int n, m;
	scanf("%d %d", &n, &m);
	int be, en, a, b;
	for (int i = 0; i < m; i++) {
		scanf("%d %d %d %d", &be, &a, &en, &b);
		insert(be + a * n, en + (b ^ 1)*n);
		insert(en + b * n, be + (a ^ 1)*n);
	}
	for (int i = 1; i <= 2*n; i++) {
		if (!dfn[i]) tarjan(i);
	}
	for (int i = 1; i <= n; i++) {
		if (clor[i] == clor[i + n]) {
			//cout << clor[i] << " " << clor[i + n] << endl;
			printf("IMPOSSIBLE\n");
			return 0;
		}
	}
	printf("POSSIBLE\n");
	for (int i = 1; i <= n; i++) {
		printf("%d ", clor[i] > clor[i + n]);
	}
	printf("\n");
	return 0;
}