2-SAT模板

K

#include <iostream>
#include <cstdio>
#include <vector>
using namespace std;
const int N = 2000010;
int n, m, head[N], ver[N << 1], nex[N << 1], tot, dfn[N], colCnt, col[N], sta[N], top, vis[N], low[N], cnt, ans[N];
inline void add (int x, int y) {
	ver[++ tot] = y;
	nex[tot] = head[x];
	head[x] = tot;
}
void tarjan (int x) {
	dfn[x] = low[x] = ++ cnt;
	sta[++ top] = x;
	vis[x] = 1;
	for (int i = head[x]; i; i = nex[i]) {
		int y = ver[i];
		if (!dfn[y]) {
			tarjan(y);
			low[x] = min(low[x], low[y]);
		} else if (vis[y])
			low[x] = min(low[x], low[y]);
	}
	if (dfn[x] == low[x]) {
		col[x] = ++ colCnt;
		vis[x] = 0;
		while (sta[top] != x) {
			col[sta[top]] = colCnt;
			vis[sta[top --]] = 0;
		}
		top --;
	}
}
int main () {
	scanf("%d%d", &n, &m);
	for (int i = 1; i <= m; i ++) {
		int x, y, a, b;
		scanf("%d%d%d%d", &x, &a, &y, &b);
		a ^= 1;
		b ^= 1;
		add(x * 2 - 1 + a, y * 2 - b);
		add(y * 2 - 1 + b, x * 2 - a);
	}
	for (int i = 1; i <= 2 * n; i ++)
		if (!dfn[i])
			tarjan(i);
	int flag = 0;
	for (int i = 1; i <= 2 * n; i += 2)
		if (col[i] == col[i + 1])
			flag = 1;
	if (flag) {
		printf("IMPOSSIBLE\n");
		return 0;
	}
	for (int i = 1; i <= n * 2; i ++) vis[i] = 0;
	vector<int> v;
	for (int i = 1; i <= n; i ++) {
		int c1 = col[i * 2 - 1], c2 = col[i * 2];
		if (vis[c1]) {
			ans[i] = 0;
			continue;
		}
		if (vis[c2]) {
			ans[i] = 1;
			continue;
		}
		if (c1 < c2) {
			ans[i] = 0;
			vis[c1] = 1;
		} else {
			ans[i] = 1;
			vis[c2] = 1;
		}
	}
	printf("POSSIBLE\n");
	for (int i = 1; i <= n; i ++) printf("%d ", ans[i]);
	printf("\n");
	return 0;
}