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// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include <vector>
namespace ui {
class AXTree;
// A class to create all possible trees with up to <n> nodes and the
// ids [1...n].
//
// There are two parts to the algorithm:
//
// The tree structure is formed as follows: without loss of generality,
// the first node becomes the root and the second node becomes its
// child. Thereafter, choose every possible parent for every other node.
//
// So for node i in (3...n), there are (i - 1) possible choices for its
// parent, for a total of (n-1)! (n minus 1 factorial) possible trees.
//
// The second optional part is the assignment of ids to the nodes in the tree.
// There are exactly n! (n factorial) permutations of the sequence 1...n,
// and each of these is assigned to every node in every possible tree.
//
// The total number of trees for a given <n>, including permutations of ids, is
// n! * (n-1)!
//
// n = 2: 2 trees
// n = 3: 12 trees
// n = 4: 144 trees
// n = 5: 2880 trees
//
// Note that the generator returns all trees with sizes *up to* <n>, which
// is a bit larger.
//
// This grows really fast! Still, it's very helpful for exhaustively testing
// tree code on smaller trees at least.
class TreeGenerator {
public:
// Will generate all trees with up to |max_node_count| nodes.
// If |permutations| is true, will return every possible permutation of
// ids, otherwise the root will always have id 1, and so on.
TreeGenerator(int max_node_count, bool permutations);
~TreeGenerator();
int UniqueTreeCount() const;
void BuildUniqueTree(int tree_index, AXTree* out_tree) const;
private:
void BuildUniqueTreeWithSize(
int node_count, int tree_index, AXTree* out_tree) const;
int max_node_count_;
bool permutations_;
int total_unique_tree_count_;
std::vector<int> unique_tree_count_by_size_;
};
} // namespace ui
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