style: updated interface of two-sat solver

Author: a1fredbao

src/alfred/graph/twosat.hpp

@@ -4,10 +4,10 @@
 #include <vector>
 
 struct TwoSAT {
+    const int n;
     std::vector<std::vector<int>> G;
     std::vector<int> dfn, low, stk, bel, in;
-    // TwoSAT(void) = default;
-    TwoSAT(int n) : G(2 * n) {}
+    TwoSAT(int _n) : n(_n), G(2 * _n) {} // 0-indexed, n nodes.
     void tarjan(int u, int &cnt, int &cc) {
         dfn[u] = low[u] = ++cnt;
         in[u] = 1, stk.push_back(u);
@@ -28,34 +28,30 @@ struct TwoSAT {
             } while (v != u);
         }
     }
-    // Add constraint: x = a or y = b.
-    inline void add(int x, bool a, int y, bool b) {
-        // size_t should = 2 * (std::max(x, y) + 1);
-        // if (G.size() < should) G.resize(should);
-        G[x << 1 | !a].push_back(y << 1 | b);
-        G[y << 1 | !b].push_back(x << 1 | a);
-    }
-    // Add constraint: x = a => y = b;
+    // Add constraint: res[x] = a => res[y] = b.
     inline void conduct(int x, bool a, int y, bool b) {
-        // size_t should = 2 * (std::max(x, y) + 1);
-        // if (G.size() < should) G.resize(should);
         G[x << 1 | a].push_back(y << 1 | b);
     }
+    // Add constraint: res[x] = a or res[y] = b.
+    inline void add(int x, bool a, int y, bool b) {
+        conduct(x, !a, y, b), conduct(y, !b, x, a);
+    }
+    // Add constraint: res[x] = res[y].
     inline void same(int x, int y) {
         conduct(x, true, y, true);
         conduct(y, true, x, true);
         conduct(x, false, y, false);
         conduct(y, false, x, false);
     }
+    // Add constraint: res[x] != res[y].
     inline void diff(int x, int y) {
         conduct(x, true, y, false);
         conduct(y, true, x, false);
         conduct(x, false, y, true);
         conduct(y, false, x, true);
     }
-    inline void set(int x, bool v) {
-        conduct(x, !v, x, v);
-    }
+    // Add constraint: res[x] = v.
+    inline void set(int x, bool v) { conduct(x, !v, x, v); }
     inline void init(void) { // find scc.
         int n = G.size(), cnt = 0, cc = 0;
         in = dfn = low = bel = std::vector<int>(n, 0);
@@ -72,7 +68,7 @@ struct TwoSAT {
         }
         return true;
     }
-    std::vector<int> solve(int n) {
+    std::vector<int> solve(void) {
         int var = G.size() / 2;
         std::vector<int> sol(n);
         for (int i = 0; i < var; i++) {

verify/verify-yosupo-graph/yosupo-two-sat.test.cpp

@@ -23,7 +23,7 @@ int main(int argc, char const *argv[]) {
 
     if (TS.has_solution()) {
         std::cout << "s SATISFIABLE\nv ";
-        std::vector<int> res = TS.solve(n);
+        std::vector<int> res = TS.solve();
         for (int i = 0; i < n; i++) {
             if (res[i] == 0) {
                 std::cout << -(i + 1) << ' ';