1 // Copyright 2014 The Chromium Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
4 
5 #include <vector>
6 
7 namespace ui {
8 
9 class AXTree;
10 
11 // A class to create all possible trees with up to <n> nodes and the
12 // ids [1...n].
13 //
14 // There are two parts to the algorithm:
15 //
16 // The tree structure is formed as follows: without loss of generality,
17 // the first node becomes the root and the second node becomes its
18 // child. Thereafter, choose every possible parent for every other node.
19 //
20 // So for node i in (3...n), there are (i - 1) possible choices for its
21 // parent, for a total of (n-1)! (n minus 1 factorial) possible trees.
22 //
23 // The second optional part is the assignment of ids to the nodes in the tree.
24 // There are exactly n! (n factorial) permutations of the sequence 1...n,
25 // and each of these is assigned to every node in every possible tree.
26 //
27 // The total number of trees for a given <n>, including permutations of ids, is
28 // n! * (n-1)!
29 //
30 // n = 2: 2 trees
31 // n = 3: 12 trees
32 // n = 4: 144 trees
33 // n = 5: 2880 trees
34 //
35 // Note that the generator returns all trees with sizes *up to* <n>, which
36 // is a bit larger.
37 //
38 // This grows really fast! Still, it's very helpful for exhaustively testing
39 // tree code on smaller trees at least.
40 class TreeGenerator {
41  public:
42   // Will generate all trees with up to |max_node_count| nodes.
43   // If |permutations| is true, will return every possible permutation of
44   // ids, otherwise the root will always have id 1, and so on.
45   TreeGenerator(int max_node_count, bool permutations);
46   ~TreeGenerator();
47 
48   int UniqueTreeCount() const;
49 
50   void BuildUniqueTree(int tree_index, AXTree* out_tree) const;
51 
52  private:
53   void BuildUniqueTreeWithSize(
54       int node_count, int tree_index, AXTree* out_tree) const;
55 
56   int max_node_count_;
57   bool permutations_;
58   int total_unique_tree_count_;
59   std::vector<int> unique_tree_count_by_size_;
60 };
61 
62 }  // namespace ui
63