tpl_mo_on_trees_test.cc

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/*
                          Aleph_w
 
  Data structures & Algorithms
  version 2.0.0b
  https://github.com/lrleon/Aleph-w
 
  This file is part of Aleph-w library
 
  Copyright (c) 2002-2026 Leandro Rabindranath Leon
 
  Permission is hereby granted, free of charge, to any person obtaining a copy
  of this software and associated documentation files (the "Software"), to deal
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  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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*/
 
 
# include <gtest/gtest.h>
 
# include <tpl_mo_on_trees.H>
# include <tpl_graph.H>
# include <tpl_sgraph.H>
# include <tpl_agraph.H>
# include <tpl_dynSetHash.H>
 
# include <algorithm>
# include <cstddef>
# include <random>
# include <utility>
# include <vector>
 
using namespace Aleph;
using namespace testing;
 
namespace
{
  // ── Brute-force helpers ────────────────────────────────────────
 
  // Compute parent map via DFS from tree_root
  template <class GT>
  DynMapHash<typename GT::Node*, typename GT::Node*>
  compute_parents(const GT & g, typename GT::Node * tree_root)
  {
    using Node = typename GT::Node;
    DynMapHash<Node*, Node*> parent;
    parent.insert(tree_root, nullptr);
    DynListStack<std::pair<Node*, Node*>> stk;
    stk.push({tree_root, nullptr});
    while (not stk.is_empty())
      {
        auto [cur, par] = stk.pop();
        for (auto it = typename GT::Node_Arc_Iterator(cur);
             it.has_curr(); it.next_ne())
          {
            auto * a = it.get_curr();
            auto * nb = g.get_connected_node(a, cur);
            if (nb != par)
              {
                parent.insert(nb, cur);
                stk.push({nb, cur});
              }
          }
      }
    return parent;
  }
 
  // Brute-force distinct count over subtree of subtree_root
  template <class GT>
  size_t brute_subtree_distinct(
      const GT & g,
      DynMapHash<typename GT::Node*,
                 typename GT::Node*> & parent,
      typename GT::Node * subtree_root)
  {
    using Node = typename GT::Node;
    DynSetHash<typename Node::Node_Type> seen;
    DynListStack<Node*> stk;
    stk.push(subtree_root);
    while (not stk.is_empty())
      {
        auto * cur = stk.pop();
        seen.insert(cur->get_info());
        for (auto it = typename GT::Node_Arc_Iterator(cur);
             it.has_curr(); it.next_ne())
          {
            auto * a = it.get_curr();
            auto * nb = g.get_connected_node(a, cur);
            if (nb != parent.find(cur))
              stk.push(nb);
          }
      }
    return seen.size();
  }
 
  // Brute-force distinct count on path u→v
  template <class GT>
  size_t brute_path_distinct(
      const GT & g,
      DynMapHash<typename GT::Node*,
                 typename GT::Node*> & parent,
      typename GT::Node * u, typename GT::Node * v)
  {
    (void) g;
    using Node = typename GT::Node;
    // Collect ancestors of u
    DynSetHash<Node*> anc_u;
    for (auto * p = u; p; p = parent.find(p))
      anc_u.insert(p);
    // Find LCA
    Node * lca_node = v;
    while (!anc_u.has(lca_node))
      lca_node = parent.find(lca_node);
    // Collect values on path
    DynSetHash<typename Node::Node_Type> vals;
    for (auto * p = u; p != lca_node; p = parent.find(p))
      vals.insert(p->get_info());
    for (auto * p = v; p != lca_node; p = parent.find(p))
      vals.insert(p->get_info());
    vals.insert(lca_node->get_info());
    return vals.size();
  }
 
  // ── Tree builder helper ────────────────────────────────────────
 
  // Build a random tree with n nodes, values in [0, max_val)
  // Returns (graph, root, array_of_all_nodes)
  template <class GT>
  struct TreeInfo
  {
    GT g;
    typename GT::Node * root;
    Array<typename GT::Node *> nodes;
  };
 
  template <class GT>
  TreeInfo<GT> build_random_tree(size_t n, int max_val, std::mt19937 & rng)
  {
    TreeInfo<GT> info;
    if (n == 0)
      {
        info.root = nullptr;
        return info;
      }
 
    info.nodes = Array<typename GT::Node *>::create(n);
    for (size_t i = 0; i < n; ++i)
      info.nodes[i] = info.g.insert_node(static_cast<int>(rng() % max_val));
 
    // Build a random tree: for each node i>0, pick a random parent
    // from [0, i)
    for (size_t i = 1; i < n; ++i)
      {
        size_t parent_idx = rng() % i;
        info.g.insert_arc(info.nodes[parent_idx], info.nodes[i]);
      }
 
    info.root = info.nodes[0];
    return info;
  }
 
  // ── Path-based chain builder (for deterministic tests) ─────────
 
  //   0 — 1 — 2 — ... — (n-1)
  //   values: v[i]
  template <class GT>
  TreeInfo<GT> build_chain(const Array<int> & vals)
  {
    TreeInfo<GT> info;
    info.nodes = Array<typename GT::Node *>::create(vals.size());
    for (size_t i = 0; i < vals.size(); ++i)
      info.nodes[i] = info.g.insert_node(vals[i]);
 
    for (size_t i = 1; i < vals.size(); ++i)
      info.g.insert_arc(info.nodes[i-1], info.nodes[i]);
    info.root = info.nodes.is_empty() ? nullptr : info.nodes[0];
    return info;
  }
 
} // namespace
 
// =================================================================
// Structural tests
// =================================================================
 
TEST(MoOnTrees, EmptyGraph)
{
  List_Graph<Graph_Node<int>, Graph_Arc<Empty_Class>> g;
  EXPECT_EQ(g.vsize(), 0u);
  EXPECT_EQ(g.esize(), 0u);
  GTEST_SKIP() << "Gen_Mo_On_Trees requires a non-null root node; "
               << "empty-graph constructor semantics are undefined.";
}
 
TEST(MoOnTrees, SingleNode)
{
  using G = List_Graph<Graph_Node<int>, Graph_Arc<Empty_Class>>;
  G g;
  auto * r = g.insert_node(42);
  Distinct_Count_Mo_On_Trees<G> mot(g, r);
 
  EXPECT_EQ(mot.size(), 1u);
  EXPECT_FALSE(mot.is_empty());
 
  auto sub = mot.subtree_solve({r});
  EXPECT_EQ(sub(0), 1u);
 
  auto path = mot.path_solve({{r, r}});
  EXPECT_EQ(path(0), 1u);
}
 
TEST(MoOnTrees, TwoNodes)
{
  using G = List_Graph<Graph_Node<int>, Graph_Arc<Empty_Class>>;
  G g;
  auto * a = g.insert_node(10);
  auto * b = g.insert_node(10);
  g.insert_arc(a, b);
 
  Distinct_Count_Mo_On_Trees<G> mot(g, a);
 
  auto sub = mot.subtree_solve({a, b});
  EXPECT_EQ(sub(0), 1u); // subtree(a) = {10, 10} → 1 distinct
  EXPECT_EQ(sub(1), 1u); // subtree(b) = {10} → 1 distinct
 
  auto path = mot.path_solve({{a, b}});
  EXPECT_EQ(path(0), 1u); // path a→b = {10, 10} → 1 distinct
}
 
TEST(MoOnTrees, TwoNodesDifferentValues)
{
  using G = List_Graph<Graph_Node<int>, Graph_Arc<Empty_Class>>;
  G g;
  auto * a = g.insert_node(10);
  auto * b = g.insert_node(20);
  g.insert_arc(a, b);
 
  Distinct_Count_Mo_On_Trees<G> mot(g, a);
 
  auto sub = mot.subtree_solve({a, b});
  EXPECT_EQ(sub(0), 2u);
  EXPECT_EQ(sub(1), 1u);
 
  auto path = mot.path_solve({{a, b}, {a, a}, {b, b}});
  EXPECT_EQ(path(0), 2u);
  EXPECT_EQ(path(1), 1u);
  EXPECT_EQ(path(2), 1u);
}
 
TEST(MoOnTrees, InvalidNodeThrows)
{
  using G = List_Graph<Graph_Node<int>, Graph_Arc<Empty_Class>>;
  G g;
  auto * a = g.insert_node(1);
  auto * b = g.insert_node(2);
  g.insert_arc(a, b);
 
  // Create a node NOT in the graph
  G g2;
  auto * alien = g2.insert_node(99);
 
  Distinct_Count_Mo_On_Trees<G> mot(g, a);
 
  EXPECT_THROW(mot.subtree_solve({alien}), std::domain_error);
  EXPECT_THROW(mot.path_solve({{a, alien}}), std::domain_error);
}
 
// =================================================================
// Subtree query tests — List_Graph
// =================================================================
 
TEST(MoOnTreesSubtree, SmallTreeListGraph)
{
  /*      1 (root)
   *     / \
   *    2   1
   *   / \
   *  3   2
   */
  using G = List_Graph<Graph_Node<int>, Graph_Arc<Empty_Class>>;
  G g;
  auto * r  = g.insert_node(1);
  auto * a  = g.insert_node(2);
  auto * b  = g.insert_node(1);
  auto * c  = g.insert_node(3);
  auto * d  = g.insert_node(2);
  g.insert_arc(r, a);
  g.insert_arc(r, b);
  g.insert_arc(a, c);
  g.insert_arc(a, d);
 
  auto parent = compute_parents(g, r);
 
  Distinct_Count_Mo_On_Trees<G> mot(g, r);
  auto ans = mot.subtree_solve({r, a, b, c, d});
 
  EXPECT_EQ(ans(0), brute_subtree_distinct(g, parent, r));
  EXPECT_EQ(ans(1), brute_subtree_distinct(g, parent, a));
  EXPECT_EQ(ans(2), brute_subtree_distinct(g, parent, b));
  EXPECT_EQ(ans(3), brute_subtree_distinct(g, parent, c));
  EXPECT_EQ(ans(4), brute_subtree_distinct(g, parent, d));
 
  // Manual verification
  EXPECT_EQ(ans(0), 3u); // {1,2,3}
  EXPECT_EQ(ans(1), 2u); // {2,3}
  EXPECT_EQ(ans(2), 1u); // {1}
  EXPECT_EQ(ans(3), 1u); // {3}
  EXPECT_EQ(ans(4), 1u); // {2}
}
 
// =================================================================
// Path query tests — List_SGraph
// =================================================================
 
TEST(MoOnTreesPath, ChainListSGraph)
{
  // Chain: 1 — 2 — 3 — 4 — 5
  using G = List_SGraph<Graph_Snode<int>, Graph_Sarc<Empty_Class>>;
  auto info = build_chain<G>({1, 2, 3, 4, 5});
  auto & g = info.g;
  auto & n = info.nodes;
  auto parent = compute_parents(g, n[0]);
 
  Distinct_Count_Mo_On_Trees<G> mot(g, n[0]);
 
  auto ans = mot.path_solve({
      {n[0], n[4]},   // 1→2→3→4→5, 5 distinct
      {n[1], n[3]},   // 2→3→4, 3 distinct
      {n[0], n[0]},   // just 1, 1 distinct
      {n[2], n[4]}    // 3→4→5, 3 distinct
  });
 
  EXPECT_EQ(ans(0), 5u);
  EXPECT_EQ(ans(1), 3u);
  EXPECT_EQ(ans(2), 1u);
  EXPECT_EQ(ans(3), 3u);
 
  for (size_t i = 0; i < 4; ++i)
    {
      auto [u, v] = std::pair{
        i == 0 ? n[0] : i == 1 ? n[1] : i == 2 ? n[0] : n[2],
        i == 0 ? n[4] : i == 1 ? n[3] : i == 2 ? n[0] : n[4]};
      EXPECT_EQ(ans(i), brute_path_distinct(g, parent, u, v))
        << "query " << i;
    }
}
 
TEST(MoOnTreesPath, StarListSGraph)
{
  // Star:  center = 1, leaves = 2, 2, 3, 3, 4
  using G = List_SGraph<Graph_Snode<int>, Graph_Sarc<Empty_Class>>;
  G g;
  auto * center = g.insert_node(1);
  auto * l1 = g.insert_node(2);
  auto * l2 = g.insert_node(2);
  auto * l3 = g.insert_node(3);
  auto * l4 = g.insert_node(3);
  auto * l5 = g.insert_node(4);
  g.insert_arc(center, l1);
  g.insert_arc(center, l2);
  g.insert_arc(center, l3);
  g.insert_arc(center, l4);
  g.insert_arc(center, l5);
 
  auto parent = compute_parents(g, center);
  Distinct_Count_Mo_On_Trees<G> mot(g, center);
 
  auto ans = mot.path_solve({
      {l1, l2},       // 2→1→2: {1,2} = 2
      {l1, l5},       // 2→1→4: {1,2,4} = 3
      {l3, l4},       // 3→1→3: {1,3} = 2
      {center, l5}    // 1→4: {1,4} = 2
  });
 
  EXPECT_EQ(ans(0), brute_path_distinct(g, parent, l1, l2));
  EXPECT_EQ(ans(1), brute_path_distinct(g, parent, l1, l5));
  EXPECT_EQ(ans(2), brute_path_distinct(g, parent, l3, l4));
  EXPECT_EQ(ans(3), brute_path_distinct(g, parent, center, l5));
}
 
// =================================================================
// Array_Graph tests
// =================================================================
 
TEST(MoOnTreesSubtree, SmallTreeArrayGraph)
{
  /*      10 (root)
   *     /    \
   *   20      30
   *  / \
   * 10  20
   */
  using G = Array_Graph<Graph_Anode<int>, Graph_Aarc<Empty_Class>>;
  G g;
  auto * r  = g.insert_node(10);
  auto * a  = g.insert_node(20);
  auto * b  = g.insert_node(30);
  auto * c  = g.insert_node(10);
  auto * d  = g.insert_node(20);
  g.insert_arc(r, a);
  g.insert_arc(r, b);
  g.insert_arc(a, c);
  g.insert_arc(a, d);
 
  auto parent = compute_parents(g, r);
 
  Distinct_Count_Mo_On_Trees<G> mot(g, r);
  auto sub = mot.subtree_solve({r, a, b});
  EXPECT_EQ(sub(0), brute_subtree_distinct(g, parent, r));
  EXPECT_EQ(sub(1), brute_subtree_distinct(g, parent, a));
  EXPECT_EQ(sub(2), brute_subtree_distinct(g, parent, b));
 
  EXPECT_EQ(sub(0), 3u); // {10,20,30}
  EXPECT_EQ(sub(1), 2u); // {10,20}
  EXPECT_EQ(sub(2), 1u); // {30}
 
  auto path = mot.path_solve({{c, d}, {c, b}});
  EXPECT_EQ(path(0), brute_path_distinct(g, parent, c, d));
  EXPECT_EQ(path(1), brute_path_distinct(g, parent, c, b));
}
 
// =================================================================
// Stress tests (random trees, brute-force verification)
// =================================================================
 
template <class GT>
class MoOnTreesStress : public Test {};
 
using GraphTypes = Types<
    List_Graph<Graph_Node<int>, Graph_Arc<Empty_Class>>,
    List_SGraph<Graph_Snode<int>, Graph_Sarc<Empty_Class>>,
    Array_Graph<Graph_Anode<int>, Graph_Aarc<Empty_Class>>
>;
 
TYPED_TEST_SUITE(MoOnTreesStress, GraphTypes);
 
TYPED_TEST(MoOnTreesStress, SubtreeRandomSmall)
{
  using G = TypeParam;
  std::mt19937 rng(123);
  auto info = build_random_tree<G>(50, 10, rng);
  auto & g = info.g;
  auto parent = compute_parents(g, info.root);
 
  Distinct_Count_Mo_On_Trees<G> mot(g, info.root);
 
  // Query all nodes
  auto queries = Array<typename G::Node*>::create(info.nodes.size());
  for (size_t i = 0; i < info.nodes.size(); ++i)
    queries(i) = info.nodes[i];
 
  auto ans = mot.subtree_solve(queries);
 
  for (size_t i = 0; i < info.nodes.size(); ++i)
    EXPECT_EQ(ans(i), brute_subtree_distinct(g, parent, info.nodes[i]))
      << "node " << i;
}
 
TYPED_TEST(MoOnTreesStress, PathRandomSmall)
{
  using G = TypeParam;
  std::mt19937 rng(456);
  auto info = build_random_tree<G>(50, 10, rng);
  auto & g = info.g;
  auto parent = compute_parents(g, info.root);
  const size_t n = info.nodes.size();
 
  Distinct_Count_Mo_On_Trees<G> mot(g, info.root);
 
  // Generate 200 random path queries
  const size_t Q = 200;
  auto queries = Array<std::pair<typename G::Node*,
                                 typename G::Node*>>::create(Q);
  for (size_t i = 0; i < Q; ++i)
    queries(i) = {info.nodes[rng() % n], info.nodes[rng() % n]};
 
  auto ans = mot.path_solve(queries);
 
  for (size_t i = 0; i < Q; ++i)
    EXPECT_EQ(ans(i), brute_path_distinct(g, parent,
                                          queries(i).first,
                                          queries(i).second))
      << "query " << i;
}
 
TYPED_TEST(MoOnTreesStress, SubtreeRandomMedium)
{
  using G = TypeParam;
  std::mt19937 rng(789);
  auto info = build_random_tree<G>(500, 20, rng);
  auto & g = info.g;
  auto parent = compute_parents(g, info.root);
  const size_t n = info.nodes.size();
 
  Distinct_Count_Mo_On_Trees<G> mot(g, info.root);
 
  const size_t Q = 500;
  auto queries = Array<typename G::Node*>::create(Q);
  for (size_t i = 0; i < Q; ++i)
    queries(i) = info.nodes[rng() % n];
 
  auto ans = mot.subtree_solve(queries);
 
  for (size_t i = 0; i < Q; ++i)
    EXPECT_EQ(ans(i), brute_subtree_distinct(g, parent, queries(i)))
      << "query " << i;
}
 
TYPED_TEST(MoOnTreesStress, PathRandomMedium)
{
  using G = TypeParam;
  std::mt19937 rng(101112);
  auto info = build_random_tree<G>(500, 20, rng);
  auto & g = info.g;
  auto parent = compute_parents(g, info.root);
  const size_t n = info.nodes.size();
 
  Distinct_Count_Mo_On_Trees<G> mot(g, info.root);
 
  const size_t Q = 1000;
  auto queries = Array<std::pair<typename G::Node*,
                                 typename G::Node*>>::create(Q);
  for (size_t i = 0; i < Q; ++i)
    queries(i) = {info.nodes[rng() % n], info.nodes[rng() % n]};
 
  auto ans = mot.path_solve(queries);
 
  for (size_t i = 0; i < Q; ++i)
    EXPECT_EQ(ans(i), brute_path_distinct(g, parent,
                                          queries(i).first,
                                          queries(i).second))
      << "query " << i;
}
 
// =================================================================
// Powerful array policy on trees
// =================================================================
 
TEST(MoOnTreesPowerful, ChainPath)
{
  // Chain: 1 — 2 — 1 — 3
  // Path (0→3): values {1,2,1,3}, cnt = {1:2, 2:1, 3:1}
  //   power = 4*1 + 1*2 + 1*3 = 9
  using G = List_Graph<Graph_Node<int>, Graph_Arc<Empty_Class>>;
  auto info = build_chain<G>({1, 2, 1, 3});
  auto & n = info.nodes;
 
  Powerful_Array_Mo_On_Trees<G> mot(info.g, n[0]);
 
  auto ans = mot.path_solve({{n[0], n[3]}});
  EXPECT_EQ(ans(0), 9LL);
 
  // Subtree of root = whole tree = same answer
  auto sub = mot.subtree_solve({n[0]});
  EXPECT_EQ(sub(0), 9LL);
}
 
// =================================================================
// Deep chain (regression: iterative DFS handles deep trees)
// =================================================================
 
TEST(MoOnTrees, DeepChain)
{
  using G = List_Graph<Graph_Node<int>, Graph_Arc<Empty_Class>>;
  const size_t N = 5000;
  G g;
  std::vector<typename G::Node*> nodes;
  for (size_t i = 0; i < N; ++i)
    nodes.push_back(g.insert_node(static_cast<int>(i % 7)));
  for (size_t i = 1; i < N; ++i)
    g.insert_arc(nodes[i-1], nodes[i]);
 
  Distinct_Count_Mo_On_Trees<G> mot(g, nodes[0]);
 
  // Subtree of root = all nodes
  auto sub = mot.subtree_solve({nodes[0]});
  EXPECT_EQ(sub(0), 7u); // values 0..6
 
  // Path from first to last = all nodes
  auto path = mot.path_solve({{nodes[0], nodes[N-1]}});
  EXPECT_EQ(path(0), 7u);
}
 
// =================================================================
// No-queries edge case
// =================================================================
 
TEST(MoOnTrees, EmptyQueryArrays)
{
  using G = List_Graph<Graph_Node<int>, Graph_Arc<Empty_Class>>;
  G g;
  auto * r = g.insert_node(1);
  Distinct_Count_Mo_On_Trees<G> mot(g, r);
 
  auto sub = mot.subtree_solve(Array<typename G::Node*>());
  EXPECT_EQ(sub.size(), 0u);
 
  auto path = mot.path_solve(
      Array<std::pair<typename G::Node*, typename G::Node*>>());
  EXPECT_EQ(path.size(), 0u);
}
 
// =================================================================
// Tree_Node tests
// =================================================================
 
TEST(MoOnTreeNode, SingleNode)
{
  using TN = Tree_Node<int>;
  auto * r = new TN(42);
  Distinct_Count_Mo_On_Tree_Node<int> mot(r);
  EXPECT_EQ(mot.size(), 1u);
 
  auto sub = mot.subtree_solve({r});
  EXPECT_EQ(sub(0), 1u);
 
  auto path = mot.path_solve({{r, r}});
  EXPECT_EQ(path(0), 1u);
 
  destroy_tree(r);
}
 
TEST(MoOnTreeNode, SmallTreeSubtree)
{
  using TN = Tree_Node<int>;
  //       r(1)
  //      / | \          .
  //   a(2) b(1) c(3)
  //   / \       |
  // d(4) e(2)  f(1)
  // |
  // g(5)
  auto * r = new TN(1);
  auto * a = new TN(2);
  auto * b = new TN(1);
  auto * c = new TN(3);
  auto * d = new TN(4);
  auto * e = new TN(2);
  auto * f = new TN(1);
  auto * g = new TN(5);
 
  r->insert_rightmost_child(a);
  r->insert_rightmost_child(b);
  r->insert_rightmost_child(c);
  a->insert_rightmost_child(d);
  a->insert_rightmost_child(e);
  c->insert_rightmost_child(f);
  d->insert_rightmost_child(g);
 
  Distinct_Count_Mo_On_Tree_Node<int> mot(r);
  EXPECT_EQ(mot.size(), 8u);
 
  auto sub = mot.subtree_solve({r, a, b, c, d, e, f, g});
  EXPECT_EQ(sub(0), 5u);  // root: {1,2,1,3,4,2,1,5} → 5
  EXPECT_EQ(sub(1), 3u);  // a: {2,4,5,2} → 3
  EXPECT_EQ(sub(2), 1u);  // b: {1} → 1
  EXPECT_EQ(sub(3), 2u);  // c: {3,1} → 2
  EXPECT_EQ(sub(4), 2u);  // d: {4,5} → 2
  EXPECT_EQ(sub(5), 1u);  // e: {2} → 1
  EXPECT_EQ(sub(6), 1u);  // f: {1} → 1
  EXPECT_EQ(sub(7), 1u);  // g: {5} → 1
 
  destroy_tree(r);
}
 
TEST(MoOnTreeNode, SmallTreePath)
{
  using TN = Tree_Node<int>;
  // Same tree as above
  auto * r = new TN(1);
  auto * a = new TN(2);
  auto * b = new TN(1);
  auto * c = new TN(3);
  auto * d = new TN(4);
  auto * e = new TN(2);
  auto * f = new TN(1);
  auto * g = new TN(5);
 
  r->insert_rightmost_child(a);
  r->insert_rightmost_child(b);
  r->insert_rightmost_child(c);
  a->insert_rightmost_child(d);
  a->insert_rightmost_child(e);
  c->insert_rightmost_child(f);
  d->insert_rightmost_child(g);
 
  Distinct_Count_Mo_On_Tree_Node<int> mot(r);
 
  auto path = mot.path_solve({{g, f}, {e, b}, {d, c}, {r, r}, {a, g}});
  // g→f: g(5)→d(4)→a(2)→r(1)→c(3)→f(1) → {5,4,2,1,3} = 5
  EXPECT_EQ(path(0), 5u);
  // e→b: e(2)→a(2)→r(1)→b(1) → {2,1} = 2
  EXPECT_EQ(path(1), 2u);
  // d→c: d(4)→a(2)→r(1)→c(3) → {4,2,1,3} = 4
  EXPECT_EQ(path(2), 4u);
  // r→r: {1} = 1
  EXPECT_EQ(path(3), 1u);
  // a→g: a(2)→d(4)→g(5) → {2,4,5} = 3
  EXPECT_EQ(path(4), 3u);
 
  destroy_tree(r);
}
 
TEST(MoOnTreeNode, StressRandomSubtree)
{
  using TN = Tree_Node<int>;
  const size_t N = 200;
  const int max_val = 10;
 
  std::mt19937 rng(54321);
  std::uniform_int_distribution<int> val_dist(0, max_val - 1);
  std::uniform_int_distribution<size_t> parent_dist;
 
  // Build random tree
  std::vector<TN*> nodes(N);
  nodes[0] = new TN(val_dist(rng));
  for (size_t i = 1; i < N; ++i)
    {
      nodes[i] = new TN(val_dist(rng));
      size_t par = parent_dist(rng) % i;
      nodes[par]->insert_rightmost_child(nodes[i]);
    }
 
  Distinct_Count_Mo_On_Tree_Node<int> mot(nodes[0]);
  EXPECT_EQ(mot.size(), N);
 
  // Brute-force subtree distinct: DFS collecting values
  auto brute_subtree = [&](TN * sub_root) -> size_t
    {
      DynSetHash<int> seen;
      std::vector<TN*> stk;
      stk.push_back(sub_root);
      while (!stk.empty())
        {
          auto * cur = stk.back();
          stk.pop_back();
          seen.insert(cur->get_key());
          for (auto * ch = cur->get_left_child(); ch != nullptr;
               ch = ch->get_right_sibling())
            stk.push_back(ch);
        }
      return seen.size();
    };
 
  // Query every node
  auto qroots = Array<TN*>::create(N);
  for (size_t i = 0; i < N; ++i)
    qroots(i) = nodes[i];
 
  auto ans = mot.subtree_solve(qroots);
  for (size_t i = 0; i < N; ++i)
    EXPECT_EQ(ans(i), brute_subtree(nodes[i]))
      << "Mismatch at subtree node " << i;
 
  destroy_tree(nodes[0]);
}
 
TEST(MoOnTreeNode, NullRootThrows)
{
  EXPECT_THROW(
    Distinct_Count_Mo_On_Tree_Node<int>(nullptr),
    std::domain_error);
}
 
TEST(MoOnTreeNode, EmptyQueryArrays)
{
  using TN = Tree_Node<int>;
  auto * r = new TN(1);
  Distinct_Count_Mo_On_Tree_Node<int> mot(r);
 
  auto sub = mot.subtree_solve(Array<TN*>());
  EXPECT_EQ(sub.size(), 0u);
 
  auto path = mot.path_solve(Array<std::pair<TN*, TN*>>());
  EXPECT_EQ(path.size(), 0u);
 
  destroy_tree(r);
}