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source/DS/UF_QUndo.cpp

@@ -0,0 +1,60 @@
+struct dsu_pb {
+    const int N;
+    vi par; stack<pair<pii, pii> > s;
+     
+    dsu_pb(int N):N(N), par(N) {
+        fors(i, 0, N-1) par[i] = -1;
+    }
+    int root(int i) {
+        if(par[i] < 0) return i;
+        return root(par[i]);
+    }
+    bool join(int i, int j) {
+        i = root(i); j = root(j);
+        s.push({{i, par[i]}, {j, par[j]}});
+        if(i == j) return false;
+        if(-par[i] < -par[j]) swap(i, j);
+        par[i] += par[j]; par[j] = i;
+        return true;
+    }
+
+protected:
+    void unjoin() {
+        assert(!s.empty());
+        auto [i, j] = s.top(); s.pop();
+        par[i.fi] = i.se; par[j.fi] = j.se;
+    }
+};
+
+struct dsu_pf : public dsu_pb {    
+    vector<pair<bool, pii> > st;          // fi==0 -> B type, fi==1 -> A type
+    vector<pair<bool, pii> > tmp[2];
+    int A=0, B=0;
+    dsu_pf(int N):dsu_pb(N){}
+    
+    bool join(int i, int j) {
+        st.pb({0, {i, j}}); B++;
+        return dsu_pb::join(i, j);
+    }
+    void pop_front() {
+        assert(!st.empty());
+        if(A == 0) {
+            forr(i, B) unjoin();
+            A = B; B = 0; reverse(all(st));
+            for(auto &[b, p]:st) b = 1, dsu_pb::join(p.fi, p.se);
+        }
+        else if(st.back().fi == false) {
+            tmp[st.back().fi].pb(st.back()); st.pop_back(); unjoin(); 
+            while(tmp[0].size() != tmp[1].size() and (unsigned) A != tmp[1].size()) {
+                tmp[st.back().fi].pb(st.back());
+                st.pop_back();
+                unjoin();
+            } 
+            for(auto i:{0, 1}) reverse(all(tmp[i]));
+            for(auto i:{0, 1}) for(auto v:tmp[i]) 
+                st.pb(v), dsu_pb::join(v.se.fi, v.se.se);
+            tmp[0].clear(); tmp[1].clear();
+        }
+        A--; st.pop_back(); unjoin();
+    }
+};