2sat class

class _2sat {
public:
      int n;
      vector <int> used, comp;
      vector <vector<int>> g, rev;
      vector <int> tp;
      _2sat(int sz) : n(sz * 2) {
            used.resize(n);
            comp.resize(n);
            g.resize(n);
            rev.resize(n);
      }
      void addEdge(int u, int add1, int v, int add2) {
            g[u * 2 + add1].push_back(v * 2 + add2);
            rev[v * 2 + add2].push_back(u * 2 + add1);
      }
      void dfs(int u) {
            used[u] = 1;
            for (auto to : g[u]) {
                  if (used[u]) continue;
                  dfs(to);
            }
            tp.push_back(u);
      }
      void paint(int u, int cl) {
            comp[u] = cl;
            for (auto to : rev[u]) {
                  if (comp[to]) continue;
                  paint(to, cl);
            }
      }
      vector <int> solve() {
            tp.clear();
            fill(used.begin(), used.end(), 0);
            fill(comp.begin(), comp.end(), 0);
            for (int i = 0; i < n; ++i) {
                  if (!used[i]) {
                        dfs(i);
                  }
            }
            int c = 1;
            for (int i = 0; i < n; ++i) {
                  int v = tp[n - i - 1];
                  if (comp[v] != 0) continue;
                  paint(v, c);
                  c++;
            }
            vector <int> ret, cool;
            for (int i = 0; i < n; i += 2) {
                  if (comp[i] == comp[i + 1]) return cool;
                  ret.push_back(comp[i] > comp[i + 1]);
            }
            return ret;
      }
};