DFS_recursive_inorder_btree in Julia would crash for singe-branch tree

[jiegillet]

In the code below, I think the case of single branch binary trees was not considered. It is checking >2 and >0 but not ==1 yet it uses [1]. We should add a case for single branch (which I realize is not well defined for here since we don't know if it's a left or right branch).

algorithm-archive/chapters/tree_traversal/code/julia/Tree.jl

Lines 28 to 43 in d9d8405

	# This assumes only 2 children
	function DFS_recursive_inorder_btree(n::Node)
	if (length(n.children) > 2)
	println("Not a binary tree!")
	exit(1)
	end
	if (length(n.children) > 0)
	DFS_recursive_inorder_btree(n.children[0])
	println(n.ID)
	DFS_recursive_inorder_btree(n.children[1])
	else
	println(n.ID)
	end
	end

[leios]

Yeah, I see what you are saying. We might want to rework this section so that the children are not a vector of child nodes, but instead left and right branches, which are more standard for binary trees anyway.

The reason I went with this implementation to begin with is because we defined node earlier in the chapter, but we could define a binary_node for the binary tree cases and go with that too.

[jiegillet]

I think it's OK to go with that implementation for now since it's used throughout the chapter and in order is just a special case quickly covered. Just add the case length(n.children) == 1 with a comment saying "for simplicity we assume it's a left branch" or something.

[leios]

Yeah. I think that's probably fine in this case, but I know several people have wanted me to split the chapter into two anyway, so maybe this is a good chance to do so?

[jiegillet]

Yeah, why not. Maybe talk a bit about binary search trees or something to flesh it out.

[jiegillet]

Fixed in #172