source: branches/PersistenceOverhaul/HeuristicLab.ExtLibs/HeuristicLab.NRefactory/5.5.0/NRefactory-5.5.0/Utils/TreeTraversal.cs

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// 
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// 
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// PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE
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using System;
using System.Collections.Generic;

namespace ICSharpCode.NRefactory.Utils
{
  /// <summary>
  /// Static helper methods for traversing trees.
  /// </summary>
  public static class TreeTraversal
  {
    /// <summary>
    /// Converts a tree data structure into a flat list by traversing it in pre-order.
    /// </summary>
    /// <param name="root">The root element of the tree.</param>
    /// <param name="recursion">The function that gets the children of an element.</param>
    /// <returns>Iterator that enumerates the tree structure in pre-order.</returns>
    public static IEnumerable<T> PreOrder<T>(T root, Func<T, IEnumerable<T>> recursion)
    {
      return PreOrder(new T[] { root }, recursion);
    }
    
    /// <summary>
    /// Converts a tree data structure into a flat list by traversing it in pre-order.
    /// </summary>
    /// <param name="input">The root elements of the forest.</param>
    /// <param name="recursion">The function that gets the children of an element.</param>
    /// <returns>Iterator that enumerates the tree structure in pre-order.</returns>
    public static IEnumerable<T> PreOrder<T>(IEnumerable<T> input, Func<T, IEnumerable<T>> recursion)
    {
      Stack<IEnumerator<T>> stack = new Stack<IEnumerator<T>>();
      try {
        stack.Push(input.GetEnumerator());
        while (stack.Count > 0) {
          while (stack.Peek().MoveNext()) {
            T element = stack.Peek().Current;
            yield return element;
            IEnumerable<T> children = recursion(element);
            if (children != null) {
              stack.Push(children.GetEnumerator());
            }
          }
          stack.Pop().Dispose();
        }
      } finally {
        while (stack.Count > 0) {
          stack.Pop().Dispose();
        }
      }
    }
    
    /// <summary>
    /// Converts a tree data structure into a flat list by traversing it in post-order.
    /// </summary>
    /// <param name="root">The root element of the tree.</param>
    /// <param name="recursion">The function that gets the children of an element.</param>
    /// <returns>Iterator that enumerates the tree structure in post-order.</returns>
    public static IEnumerable<T> PostOrder<T>(T root, Func<T, IEnumerable<T>> recursion)
    {
      return PostOrder(new T[] { root }, recursion);
    }
    
    /// <summary>
    /// Converts a tree data structure into a flat list by traversing it in post-order.
    /// </summary>
    /// <param name="input">The root elements of the forest.</param>
    /// <param name="recursion">The function that gets the children of an element.</param>
    /// <returns>Iterator that enumerates the tree structure in post-order.</returns>
    public static IEnumerable<T> PostOrder<T>(IEnumerable<T> input, Func<T, IEnumerable<T>> recursion)
    {
      Stack<IEnumerator<T>> stack = new Stack<IEnumerator<T>>();
      try {
        stack.Push(input.GetEnumerator());
        while (stack.Count > 0) {
          while (stack.Peek().MoveNext()) {
            T element = stack.Peek().Current;
            IEnumerable<T> children = recursion(element);
            if (children != null) {
              stack.Push(children.GetEnumerator());
            } else {
              yield return element;
            }
          }
          stack.Pop().Dispose();
          if (stack.Count > 0)
            yield return stack.Peek().Current;
        }
      } finally {
        while (stack.Count > 0) {
          stack.Pop().Dispose();
        }
      }
    }
  }
}