| | 1 | | namespace MoreStructures.RecImmTrees.Visitor; |
| | 2 | |
|
| | 3 | | /// <inheritdoc cref="BreadthFirstTraversal{TEdge, TNode}" path="//*[not(self::summary or self::remarks)]"/> |
| | 4 | | /// <summary> |
| | 5 | | /// A lazy, fully-iterative, breadth-first <see cref="IVisitStrategy{TNode, TVisitContext}"/> implementation, i.e. a |
| | 6 | | /// traversing strategy which visits all the nodes at the current depth, along any path of the tree, before going |
| | 7 | | /// deeper or shallower, exploring nodes with higher or lower depth. |
| | 8 | | /// </summary> |
| | 9 | | /// <remarks> |
| | 10 | | /// <inheritdoc cref="BreadthFirstTraversal{TEdge, TNode}" path="/remarks"/> |
| | 11 | | /// <para id="advantages"> |
| | 12 | | /// ADVANTAGES AND DISADVANTAGES |
| | 13 | | /// <br/> |
| | 14 | | /// <inheritdoc cref="DocFragments" path="/remarks/para[@id='fully-iterative-advantages']"/> |
| | 15 | | /// </para> |
| | 16 | | /// </remarks> |
| | 17 | | public class FullyIterativeBreadthFirstTraversal<TEdge, TNode> |
| | 18 | | : BreadthFirstTraversal<TEdge, TNode> |
| | 19 | | where TEdge : IRecImmDictIndexedTreeEdge<TEdge, TNode> |
| | 20 | | where TNode : IRecImmDictIndexedTreeNode<TEdge, TNode> |
| | 21 | | { |
| | 22 | |
|
| | 23 | | /// <inheritdoc |
| | 24 | | /// cref="TreeTraversal{TEdge, TNode}.Visit(TNode)" |
| | 25 | | /// path="//*[not(self::summary or self::remarks)]"/> |
| | 26 | | /// <summary> |
| | 27 | | /// <b>Lazily and iteratively</b> visits the structure of the provided <paramref name= "node" />, returning the |
| | 28 | | /// sequence of <see cref="IRecImmDictIndexedTreeNode{TEdge, TNode}"/> of the structure, in breadth-first order. |
| | 29 | | /// </summary> |
| | 30 | | /// <remarks> |
| | 31 | | /// <inheritdoc cref="FullyIterativeBreadthFirstTraversal{TEdge, TNode}" path="/remarks"/> |
| | 32 | | /// <para id="algo"> |
| | 33 | | /// ALGORITHM |
| | 34 | | /// <br/> |
| | 35 | | /// The algorithm performs a double walk: |
| | 36 | | /// <br/> |
| | 37 | | /// - The first walk is of the nodes of the tree structure and always proceeds top-down, enqueuing each |
| | 38 | | /// encountered child for each node into a "traversal" <see cref="Queue{T}"/>, which is used to reproduce the |
| | 39 | | /// breadth-first order. |
| | 40 | | /// <br/> |
| | 41 | | /// - The first walk also enqueues each encountered node into a "visit" <see cref="Queue{T}"/>, if the |
| | 42 | | /// <see cref="TreeTraversal{TEdge, TNode}.TraversalOrder"/> is <see cref="TreeTraversalOrder.ParentFirst"/>, |
| | 43 | | /// or it pushes it onto a "visit" <see cref="Stack{T}"/>, if it is |
| | 44 | | /// <see cref="TreeTraversalOrder.ChildrenFirst"/>. |
| | 45 | | /// <br/> |
| | 46 | | /// - The second walk goes through the "visit" queue/stack, yielding to the output sequence, so that the |
| | 47 | | /// client code implementing the visitor can lazily process the nodes. |
| | 48 | | /// </para> |
| | 49 | | /// <para id="complexity"> |
| | 50 | | /// COMPLEXITY |
| | 51 | | /// <br/> |
| | 52 | | /// Each of the walk goes through all the n nodes and n - 1 edges of the tree. |
| | 53 | | /// <br/> |
| | 54 | | /// Each walk uses a O(1) insertion and extraction data structure, which contains at most n elements of |
| | 55 | | /// constant size (reference to the node, reference to its parent, reference to its incoming edge). |
| | 56 | | /// <br/> |
| | 57 | | /// Time Complexity is O(n) for the first walk, when the visit queue/stack is populated and no actual node |
| | 58 | | /// visit is performed, and O(n) for the second walk, when the actual visit of all nodes is performed. |
| | 59 | | /// So O(n) in total. |
| | 60 | | /// <br/> |
| | 61 | | /// Space Complexity is O(2n) for the first walk, due to the traversal and visit queue/stack being allocated |
| | 62 | | /// and populated, and O(n) for the second walk, when the actual visit of all nodes is performed. |
| | 63 | | /// So O(n) in total. |
| | 64 | | /// </para> |
| | 65 | | /// </remarks> |
| | 66 | | public override IEnumerable<TreeTraversalVisit<TEdge, TNode>> Visit(TNode node) |
| 66 | 67 | | { |
| 66 | 68 | | switch (TraversalOrder) |
| | 69 | | { |
| | 70 | | case TreeTraversalOrder.ParentFirst: |
| 60 | 71 | | { |
| 60 | 72 | | var traversalQueue = new Queue<TreeTraversalVisit<TEdge, TNode>>(); |
| 60 | 73 | | traversalQueue.Enqueue(new(node, default, default, 0)); |
| | 74 | |
|
| 60 | 75 | | var visitQueue = new Queue<TreeTraversalVisit<TEdge, TNode>>(); |
| | 76 | |
|
| 10705 | 77 | | while (traversalQueue.Count > 0) |
| 10645 | 78 | | ProcessParentFirstTraversalQueue(traversalQueue, visitQueue); |
| | 79 | |
|
| 10532 | 80 | | while (visitQueue.Count > 0) |
| 10497 | 81 | | yield return visitQueue.Dequeue(); |
| 35 | 82 | | } |
| | 83 | |
|
| 35 | 84 | | break; |
| | 85 | |
|
| | 86 | | case TreeTraversalOrder.ChildrenFirst: |
| 4 | 87 | | { |
| 4 | 88 | | var traversalQueue = new Queue<TreeTraversalVisit<TEdge, TNode>>(); |
| 4 | 89 | | traversalQueue.Enqueue(new(node, default, default, 0)); |
| | 90 | |
|
| 4 | 91 | | var visitStack = new Stack<TreeTraversalVisit<TEdge, TNode>>(); |
| | 92 | |
|
| 45 | 93 | | while (traversalQueue.Count > 0) |
| 41 | 94 | | ProcessChildrenFirstTraversalQueue(traversalQueue, visitStack); |
| | 95 | |
|
| 45 | 96 | | while (visitStack.Count > 0) |
| 41 | 97 | | yield return visitStack.Pop(); |
| 4 | 98 | | } |
| | 99 | |
|
| 4 | 100 | | break; |
| | 101 | |
|
| | 102 | | default: |
| 2 | 103 | | throw new NotSupportedException($"{nameof(TraversalOrder)} {TraversalOrder} not supported."); |
| | 104 | | } |
| 39 | 105 | | } |
| | 106 | |
|
| | 107 | | private void ProcessParentFirstTraversalQueue( |
| | 108 | | Queue<TreeTraversalVisit<TEdge, TNode>> traversalQueue, Queue<TreeTraversalVisit<TEdge, TNode>> visitQueue) |
| 10645 | 109 | | { |
| 10645 | 110 | | var visit = traversalQueue.Dequeue(); |
| 10645 | 111 | | var (node, _, _, level) = visit; |
| | 112 | |
|
| 10645 | 113 | | visitQueue.Enqueue(visit); |
| 53105 | 114 | | foreach (var child in ChildrenSorter(visit)) |
| 10585 | 115 | | traversalQueue.Enqueue(new(child.Value, node, child.Key, level + 1)); |
| 10645 | 116 | | } |
| | 117 | |
|
| | 118 | | private void ProcessChildrenFirstTraversalQueue( |
| | 119 | | Queue<TreeTraversalVisit<TEdge, TNode>> traversalQueue, Stack<TreeTraversalVisit<TEdge, TNode>> visitStack) |
| 41 | 120 | | { |
| 41 | 121 | | var visit = traversalQueue.Dequeue(); |
| 41 | 122 | | var (node, _, _, level) = visit; |
| | 123 | |
|
| 41 | 124 | | visitStack.Push(visit); |
| 197 | 125 | | foreach (var child in ChildrenSorter(visit).Reverse()) |
| 37 | 126 | | traversalQueue.Enqueue(new(child.Value, node, child.Key, level + 1)); |
| 41 | 127 | | } |
| | 128 | | } |