update

Author: lrvideckis

library/dsu/dsu_bipartite.hpp

@@ -3,10 +3,8 @@
 //! DSU with support for parity of path to root for online
 //! bipartite check
 struct dsu_bipartite {
-  int num_sets;
   vi p, is_bi, parity;
-  dsu_bipartite(int n):
-    num_sets(n), p(n, -1), is_bi(n, 1), parity(n) {}
+  dsu_bipartite(int n): p(n, -1), is_bi(n, 1), parity(n) {}
   int f(int v) {
     if (p[v] < 0) return v;
     int root = f(p[v]);
@@ -15,17 +13,16 @@ struct dsu_bipartite {
   }
   bool join(int u, int v) {
     int root_u = f(u), root_v = f(v);
-    if (root_u == root_v) {
-      if (parity[u] == parity[v]) is_bi[root_u] = 0;
+    int new_parity = parity[v] ^ parity[u];
+    u = root_u, v = root_v;
+    if (u == v) {
+      is_bi[u] &= new_parity;
       return 0;
     }
-    if (p[root_u] > p[root_v]) {
-      swap(u, v);
-      swap(root_u, root_v);
-    }
-    is_bi[root_u] &= is_bi[root_v];
-    parity[root_v] = parity[v] ^ 1 ^ parity[u];
-    p[root_u] += p[root_v], p[root_v] = root_u, num_sets--;
+    if (p[u] > p[v]) swap(u, v);
+    is_bi[u] &= is_bi[v];
+    parity[v] = new_parity ^ 1;
+    p[u] += p[v], p[v] = u;
     return 1;
   }
   int size(int v) { return -p[f(v)]; }

tests/library_checker_aizu_tests/dsu/dsu_bipartite.test.cpp

@@ -43,7 +43,7 @@ int main() {
       adj[u].push_back(v);
       adj[v].push_back(u);
     } else cout << (dsu.f(u) == dsu.f(v)) << '\n';
-    if (rnd<int>(0, 20'000) == 0) check();
+    if (i <= 20 || rnd<int>(0, 20'000) == 0) check();
   }
   check();
   return 0;