chromium/ui/accessibility/tree_generator.h

// Copyright 2014 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef UI_ACCESSIBILITY_TREE_GENERATOR_H_
#define UI_ACCESSIBILITY_TREE_GENERATOR_H_

#include <optional>
#include <vector>

#include "ui/accessibility/ax_tree_update_forward.h"

namespace ui {

class AXTree;

// This class is only used for fuzz testing.
//
// 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 { … };

}  // namespace ui

#endif  // UI_ACCESSIBILITY_TREE_GENERATOR_H_