Uses the “The Tortoise and the Hare” algorithm to detect loops.
Description
For every step of the algorithm, the hare takes two steps and the tortoise one.
If the hare ever laps the tortoise, there must be a loop.
Parameters
$callback
callablerequired- Function that accepts ( ID, callback_arg, … ) and outputs parent_ID.
$start
intrequired- The ID to start the loop check at.
$override
arrayoptional- An array of ( ID => parent_ID, … ) to use instead of $callback.
Default:
array()
$callback_args
arrayoptional- Additional arguments to send to $callback.
Default:
array()
$_return_loop
booloptional- Return loop members or just detect presence of loop? Only set to true if you already know the given $start is part of a loop (otherwise the returned array might include branches).
Default:
false
Source
function wp_find_hierarchy_loop_tortoise_hare( $callback, $start, $override = array(), $callback_args = array(), $_return_loop = false ) {
$tortoise = $start;
$hare = $start;
$evanescent_hare = $start;
$return = array();
// Set evanescent_hare to one past hare. Increment hare two steps.
while (
$tortoise
&&
( $evanescent_hare = isset( $override[ $hare ] ) ? $override[ $hare ] : call_user_func_array( $callback, array_merge( array( $hare ), $callback_args ) ) )
&&
( $hare = isset( $override[ $evanescent_hare ] ) ? $override[ $evanescent_hare ] : call_user_func_array( $callback, array_merge( array( $evanescent_hare ), $callback_args ) ) )
) {
if ( $_return_loop ) {
$return[ $tortoise ] = true;
$return[ $evanescent_hare ] = true;
$return[ $hare ] = true;
}
// Tortoise got lapped - must be a loop.
if ( $tortoise === $evanescent_hare || $tortoise === $hare ) {
return $_return_loop ? $return : $tortoise;
}
// Increment tortoise by one step.
$tortoise = isset( $override[ $tortoise ] ) ? $override[ $tortoise ] : call_user_func_array( $callback, array_merge( array( $tortoise ), $callback_args ) );
}
return false;
}
Changelog
Version | Description |
---|---|
3.1.0 | Introduced. |
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