1 files changed, 95 insertions, 0 deletions
diff --git a/test/graph/virtualTree.cpp b/test/graph/virtualTree.cpp
new file mode 100644
index 0000000..d256760
--- /dev/null
+++ b/test/graph/virtualTree.cpp
@@ -0,0 +1,95 @@
+#include "../util.h"
+int lca(int u, int v);
+#include <graph/virtualTree.cpp>
+
+vector<int> d, par;
+void dfs(int u, vector<vector<int>>& adj, int& counter) {
+    in[u] = counter++;
+    for (int v : adj[u]) if (v != par[u]) {
+        d[v] = d[u]+1;
+        par[v] = u;
+        dfs(v, adj, counter);
+    }
+    out[u] = counter;
+}
+
+int lca(int u, int v) {
+    if (d[u] < d[v]) swap(u, v);
+    while (d[u] > d[v]) u = par[u];
+    while (u != v) u = par[u], v = par[v];
+    return u;
+}
+
+void init(vector<vector<int>>& adj) {
+    int n = (int)sz(adj);
+    d.assign(n, 0);
+    in = par = out = d;
+    int counter = 0;
+    dfs(0, adj, counter);
+}
+
+void stress_test() {
+	for (int tries = 0; tries < 50'000; tries++) {
+		int n = Random::integer<int>(1, 50);
+		Graph<NoData> g(n);
+		g.tree();
+
+		vector<vector<int>> adj(n);
+		g.forEdges([&](int a, int b){
+			adj[a].push_back(b);
+			adj[b].push_back(a);
+		});
+
+        init(adj);
+        vector<int> ind = Random::distinct(Random::integer(1, n+1), 0, n);
+        auto [idk, tree] = virtualTree(ind);
+        vector<pair<int, int>> edges;
+        for (int i=0; i<sz(idk); i++) for (int v : tree[i]) {
+            edges.emplace_back(idk[i], idk[v]);
+        }
+
+        vector<pair<int, int>> edges2;
+        vector<bool> used(n);
+        for (int u : ind) for (int v : ind) used[lca(u, v)] = true;
+        auto dfs = [&](auto& self, int u, int p, int last) -> void {
+            if (used[u]) {
+                if (last != -1) edges2.emplace_back(last, u);
+                last = u;
+            }
+            for (int v : adj[u]) if (v != p) self(self, v, u, last);
+        };
+        dfs(dfs, 0, -1, -1);
+
+        sort(all(edges)), sort(all(edges2));
+        if (edges != edges2) cerr << "WA edge list does not match" << FAIL;
+	}
+	cerr << "tested random 50'000 tests" << endl;
+}
+
+constexpr int N = 1'000'000;
+void performance_test() {
+	timer t;
+	Graph<NoData> g(N);
+	g.tree();
+	vector<vector<int>> adj(N);
+	g.forEdges([&](int a, int b){
+		adj[a].push_back(b);
+		adj[b].push_back(a);
+	});
+
+    init(adj);
+    vector<int> ind = Random::distinct(N/2, 0, N);
+
+    ll hash = 0;
+	t.start();
+    auto [idk, tree] = virtualTree(ind);
+    hash = accumulate(all(idk), 0LL);
+	t.stop();
+	if (t.time > 1000) cerr << "too slow: " << t.time << FAIL;
+	cerr << "tested performance: " << t.time << "ms (hash: " << hash << ")" << endl;
+}
+
+int main() {
+	stress_test();
+	performance_test();
+}