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BkTree: Implement (untested) remove() method

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This commit is contained in:
Starbeamrainbowlabs 2020-03-09 01:14:31 +00:00
parent 89e59cc75e
commit 2f901642fe
Signed by: sbrl
GPG key ID: 1BE5172E637709C2
1 changed files with 48 additions and 5 deletions
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51
experiments/bktree/BkTree.php
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@ -82,11 +82,13 @@ class BkTree
/**
* Adds a string to the tree.
* @param string $string The string to add.
* @param int $starting_node_id The id fo node to start insertion from. Defaults to 0 - for internal use only.
* @return int The depth at which the new node was added.
*/
public function add(string $string) : int {
public function add(string $string, int $starting_node_id = 0) : int {
// FUTURE: When we support deletes, we'll need to ensure that the root node is handled correctly
if(!$this->box->has("node|0")) {
// If the root node of the tree doesn't exist, create it
$new = new stdClass();
$new->value = $string;
$new->children = new stdClass(); // [ "id" => int, "distance" => int ]
@ -96,9 +98,12 @@ class BkTree
return 0;
}
if(!$this->box->has("node|$starting_node_id"))
throw new Exception("Error: Failed to find node with id $starting_node_id to begin insertion");
// if($string == "bunny") echo("\nStart $string\n");
$next_node = $this->box->get("node|0"); // Grab the root to start with
$next_node = $this->box->get("node|$starting_node_id"); // Grab the root to start with
$next_node_id = 0;
$depth = 0; $visted = 0;
while(true) {
@ -142,11 +147,49 @@ class BkTree
* @return bool Whether the removal was successful.
*/
public function remove(string $string) : bool {
throw new Error("Error: Not implemented");
// TODO: Remove a node from the tree.
$stack = [ [ "node" => $this->box->get("node|0"), "id" => 0 ] ];
$node_target = $stack[0]["node"];
$node_target_id = 0;
while($node_target->value !== $string) {
$distance = levenshtein($string, $node_target->value, $this->cost_insert, $this->cost_replace, $this->cost_delete);
// Failed to recurse to find the node with the value in question
if(!isset($node_target->children->$distance))
return false;
$node_target_id = $node_target->children->$distance;
$node_target = $this->box->get("node|$node_target_id");
$stack[] = [ "node" => $node_target, "id" => $node_target->children->$distance ];
}
$parent = end($stack); // The last item on the stack is the parent node
// 1. Delete the connection from parent -> target
foreach($parent["node"]->children as $distance -> $id) {
if($id == $node_target_id) {
unset($parent["node"]->children->$distance);
break;
}
}
// Save the parent node's back to disk
// Note that we do this *before* sorting out the orphans, since it's possible that $this->add() will modify it further
$this->box->set("node|{$parent["id"]}", $parent["node"]);
// 2. Iterate over the target's children (if any) and re-hang them from the parent
// NOTE: We need to be careful that the characteristics of the tree are preserved. We should test this by tracing a node's location in the tree and purposefully removing nodes in the chain and see if the results returned as still the same
//
// Hang the now orphaned children from the parent
foreach($node_target->children as $distance -> $id) {
$orphan = $this->box->get("node|$id");
// TODO: Optimise this
$this->box->delete("node|$id"); // Delete the orphan node
$this->add($orphan->value, $parent["id"]); // Re-hang it from the parent
}
// Delete the target node
$this->box->delete("node|$node_target_id");
}
/**