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digitalmars.D.learn - foreach DFS/BFS for tree data-structure?

reply =?iso-8859-1?Q?Robert_M._M=FCnch?= <robert.muench saphirion.com> writes:
I have a simple tree C data-structure that looks like this:

node {
	node parent:
	vector[node] children;
}

I would like to create two foreach algorthims, one follwing the breadth 
first search pattern and one the depth first search pattern.

Is this possible? I read about Inputranges, took a look at the RBTree 
code etc. but don't relly know/understand where to start.

-- 
Robert M. Münch
http://www.saphirion.com
smarter | better | faster
Jun 14 2018
next sibling parent rikki cattermole <rikki cattermole.co.nz> writes:
On 14/06/2018 11:31 PM, Robert M. Münch wrote:

 I have a simple tree C data-structure that looks like this:
 
 node {


struct Node {


      node parent:


Node* parent;


      vector[node] children;


Node[] children;


 }
 
 I would like to create two foreach algorthims, one follwing the breadth 
 first search pattern and one the depth first search pattern.


Here is (very roughly breadth):

auto search(Method method) {
	struct Voldermort {
		Node parent;
		size_t offset;
		
		 property {
			Node front() {
				return parent.children[offset];
			}

			bool empty() {
				return offset == parent.children.length;
			}
		}

		void popFront() {
			offset++;
		}
	}

	return Voldermort(this);
}

Depth will be a bit of a pain since you'll need to know where you have 
been at each set of children.
Jun 14 2018
prev sibling next sibling parent reply Dennis <dkorpel gmail.com> writes:
On Thursday, 14 June 2018 at 11:31:50 UTC, Robert M. Münch wrote:

 Is this possible? I read about Inputranges, took a look at the 
 RBTree code etc. but don't relly know/understand where to start.


You can also use opApply to iterate over a tree using foreach, 
see:
https://tour.dlang.org/tour/en/gems/opdispatch-opapply
Jun 14 2018
parent reply =?iso-8859-1?Q?Robert_M._M=FCnch?= <robert.muench saphirion.com> writes:
On 2018-06-14 11:46:04 +0000, Dennis said:


 On Thursday, 14 June 2018 at 11:31:50 UTC, Robert M. Münch wrote:

 Is this possible? I read about Inputranges, took a look at the RBTree 
 code etc. but don't relly know/understand where to start.


 
 You can also use opApply to iterate over a tree using foreach, see:
 https://tour.dlang.org/tour/en/gems/opdispatch-opapply


Ah... that looks very good. Need to dig a bit deeper on how to use it. Thanks.

-- 
Robert M. Münch
http://www.saphirion.com
smarter | better | faster
Jun 14 2018
parent Steven Schveighoffer <schveiguy yahoo.com> writes:
On 6/14/18 8:35 AM, Robert M. Münch wrote:

 On 2018-06-14 11:46:04 +0000, Dennis said:
 

 On Thursday, 14 June 2018 at 11:31:50 UTC, Robert M. Münch wrote:

 Is this possible? I read about Inputranges, took a look at the RBTree 
 code etc. but don't relly know/understand where to start.


 You can also use opApply to iterate over a tree using foreach, see:
 https://tour.dlang.org/tour/en/gems/opdispatch-opapply


 
 Ah... that looks very good. Need to dig a bit deeper on how to use it. 
 Thanks.
 


Just to clarify, RBTree can easily do DFS without a real stack because 
there are a finite number of children (2) for each node, and it's an 
O(1) operation to figure out which child the current node is in relation 
to the parent (am I a left child or right child?).

Now, with your C version, if your children are stored in the array 
itself, figuring out the "next" child is a matter of doing &this + 1. 
But if you are storing pointers instead, then figuring out the next 
child would be an O(n) operation.

Using the stack to track where you are (via opApply) is a valid way as 
well. You could also unroll that into a malloc'd stack, but the code is 
not as pretty of course.

-Steve
Jun 14 2018
prev sibling next sibling parent Meta <jared771 gmail.com> writes:
On Thursday, 14 June 2018 at 11:31:50 UTC, Robert M. Münch wrote:

 I have a simple tree C data-structure that looks like this:

 node {
 	node parent:
 	vector[node] children;
 }

 I would like to create two foreach algorthims, one follwing the 
 breadth first search pattern and one the depth first search 
 pattern.

 Is this possible? I read about Inputranges, took a look at the 
 RBTree code etc. but don't relly know/understand where to start.


While it's possible to do with input ranges, it's not pretty and 
I'm not sure that it's as performant as the traditional method. I 
would recommend going with one of the other suggestions in this 
thread.
Jun 14 2018
prev sibling parent Timoses <timosesu gmail.com> writes:
On Thursday, 14 June 2018 at 11:31:50 UTC, Robert M. Münch wrote:

 I have a simple tree C data-structure that looks like this:

 node {
 	node parent:
 	vector[node] children;
 }

 I would like to create two foreach algorthims, one follwing the 
 breadth first search pattern and one the depth first search 
 pattern.

 Is this possible? I read about Inputranges, took a look at the 
 RBTree code etc. but don't relly know/understand where to start.


What I found really interesting when reading Ali Çehreli's book 
'Programming in D' was using fibers for tree iteration.

Check out http://ddili.org/ders/d.en/fibers.html and skip to the 
section "Fibers in range implementations"
Jun 16 2018