chromium / chromium / src / b4754fc159b2454e05de85b33db55f8799731b0c / . / ui / accessibility / tree_generator.h

// 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 |