| // 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 |