2-SAT！！！

板子题卡了我一个点

Luogu P4782 【模板】2-SAT

#include <iostream>
#include <stack>
#include <queue>using namespace std;
const int maxn = 2e6 + 10;
struct Edge
{int nxt, to;
}edges[maxn];bool vis[maxn];
int tot;
int id;
int cols;
int in[maxn];
int col[maxn];
int dfn[maxn];
int low[maxn];
int head[maxn];
stack <int> stk;inline void add(int u, int v)
{tot++;edges[tot].nxt = head[u];edges[tot].to = v;head[u] = tot;
}
void tar(int x)
{dfn[x] = low[x] = ++id;stk.push(x);vis[x] = true;for (int i = head[x]; i; i = edges[i].nxt){int to = edges[i].to;if (!dfn[to]){tar(to);low[x] = min(low[x], low[to]);}else if (vis[to]){low[x] = min(low[x], dfn[to]);}}if (dfn[x] == low[x]){cols++;int y;do{y = stk.top();stk.pop();col[y] = cols;vis[y] = false;}while (x != y);}
}int main()
{int n, m;cin >> n >> m;for (int i = 1; i <= m; ++i){int x, a, y, b;cin >> x >> a >> y >> b;if (a == true && b == true){add(x, y + n);add(y, x + n);}if (a == false && b == false){add(x + n, y);add(y + n, x);}if (a == true && b == false){add(x, y);add(y + n, x + n);}if (a == false && b == true){add(x + n, y + n);add(y, x);}}for (int i = 1; i <= 2 * n; ++i){if (!dfn[i])tar(i);}for (int i = 1; i <= n; ++i){if (col[i] == col[i + n]){cout << "IMPOSSIBLE" << '\n';return 0;}}cout << "POSSIBLE" << '\n';for (int i = 1; i <= n; ++i){if (col[i] > col[i + n]){cout << 1 << ' ';}else{cout << 0 << ' ';}}return 0;
}