Library used to find lowest common ancestor in graphs.

1.0.0 2017-04-30 16:26 UTC


A PHP Library to find Lowest Common ancestor from a Directed Acyclic Graph.


This library is built to find the Lowest Common ancestor from a Directed Acyclic graph. It first creates a graph and then stores the parents of a node(let's call it node1) in an array(call it array1). To find the parents of node1, we use Breadth First Search traversal in reverse order, i.e, From node1 to root. Same is done with node2. Then we find the LCA by the intersection of elements from array1 and array2. The first node returned by the intersection is the LCA of the 2 nodes.


This library uses clue/graph for creation of the graph and graphp/algorithms for Breadth First Traversal.


The library can be installed via composer.

  "name": "myorg/mylib",
  "description": "A library depending on relaxed/lca",
  "require": {
    "relaxedws/lca": "dev-master"


After installation, we can perform a merge the following way:


require __DIR__ ."/vendor/autoload.php";

use Fhaculty\Graph\Graph;
use Relaxed\LCA\LowestCommonAncestor;

$graph = new Graph();

for ($i=1; $i<=6 ; $i++){
   $vertices['node_'.$i] = $graph->createVertex('node_'.$i);


$instance = new LowestCommonAncestor($graph);

$lca = $instance->find($vertices['node_3'], $vertices['node_4']);
$base = $lca->getId();


We welcome anyone to use, test, or contribute back to this project. We have extensive test coverage, but as we all know there's always bugs in software. Please file issues or pull requests with your comments or suggestions.