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Programming-Idioms

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Idiom #18 Depth-first traversal of a tree

Call a function f on every node of a tree, in depth-first prefix order

A tree having 6 nodes, rooted at node 1
func (t *Tree) Dfs(f func(*Tree)) {
	if t == nil {
		return
	}
	f(t)
	for _, child := range t.Children {
		child.Dfs(f)
	}
}

The function f is a parameter of the traversal method Dfs .
The traversal is prefix because f is applied to current node first.
func (t *Tree[L]) Dfs(f func(*Tree[L])) {
	if t == nil {
		return
	}
	f(t)
	for _, child := range t.Children {
		child.Dfs(f)
	}
}

The type parameter L is for arbitrary node label data
function dfs($f, $root)
{
    $f($root);
    foreach($root as $child)
    {
        dfs($child);
    }	
}

Here dfs is a recursive function to traverse the tree applying a function sent as the $f parameter
void dfs(const auto &tree, const auto &root)
{
	f(root);

	for (auto child : tree)
		dfs(tree, child);
}

New implementation...