递归搜索类别及其子级

Question

I have the following class:

public class Category {
    public string Name { get; set; }
    public Category Parent { get; set; }
    public string Url { get; set; }
    public List<Category> Children { get; set; }
}

Now given an instance of a Category and url. I wish to get the Category where the url matches the category or any of it's children (or their children etc).

Therefore my function would have the following signature:

public Category FindCategory(Category category, string url);

I know recursion is the way to go and i have managed to come up with a solution. However i've definitely seen it done better but i can't find where. I'd appreciate it if someone could show me the easiest and cleanest way to achieve this.

Thanks

Answer 1

In terms of recursion the answer is pretty straight forward. I would prefer the Try pattern over a null return though.

bool TryFind(string url, Category current, out Category found) {
  if (category.Url == url) {
    found = current;
    return true;
  }

  foreach (var child in current.Children) {
    if (TryFind(url, child, out found)) {
      return true;
    }
  }

  found = null;
  return false;
}

Your question mentioned you'd seen it done "better". Could you elaborate a bit on this? I'm not quite sure what you mean.

Answer 2

Here is a simple recursive algorithm:

public Category FindCategory(Category category, string url)
{
    if(category.Url == url)
    {
        return category;
    }

    Category solution = null;    

    foreach(Category child in category.Children)
    {
        solution = FindCategory(child, url);
        if(solution != null)
        {
            return solution;
        }
    }

    return null;
}

Answer 3

I suppose you could use a stack data structure. Something like:

public Category FindCategory(Category category, string url) {
    Stack<Category> categoryStack = new Stack<Category>();
    categoryStack.Push(category);
    while(categoryStack.Peek() != null) {
        Category cat = categoryStack.Pop();
        if(cat.Url == url) {
            return cat;
        }

        foreach(Category child in cat.Children) {
            categoryStack.Push(child);
        }
    }

    return null;
}