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<?php |
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namespace Fisharebest\Algorithm; |
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/** |
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* @author Greg Roach <[email protected]> |
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* @copyright (c) 2021 Greg Roach <[email protected]> |
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* @license GPL-3.0+ |
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* |
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* This program is free software: you can redistribute it and/or modify |
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* it under the terms of the GNU General Public License as published by |
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* the Free Software Foundation, either version 3 of the License, or |
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* (at your option) any later version. |
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* This program is distributed in the hope that it will be useful, |
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* but WITHOUT ANY WARRANTY; without even the implied warranty of |
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
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* GNU General Public License for more details. |
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* You should have received a copy of the GNU General Public License |
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* along with this program. If not, see <https://www.gnu.org/licenses>. |
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*/ |
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/** |
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* Class ConnectedComponent - Use a depth-first search to find connected |
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* components of an undirected graph. |
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*/ |
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class ConnectedComponent |
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{ |
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/** @var integer[][] The graph, where $graph[node1][node2]=cost */ |
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protected $graph; |
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/** @var int[] The component number for each node */ |
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protected $nodes; |
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/** @var int The next connected-component to find. */ |
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protected $component; |
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/** |
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* @param integer[][] $graph |
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*/ |
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public function __construct($graph) |
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{ |
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$this->graph = $graph; |
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$this->nodes = array_fill_keys(array_keys($graph), 0); |
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$this->component = 0; |
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} |
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/** |
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* An array of components (arrays). |
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* |
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* @return array |
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*/ |
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public function findConnectedComponents() |
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{ |
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// Find the first unallocated node |
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$node = array_search(0, $this->nodes, true); |
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while ($node !== false) { |
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// Find the next connected-component. |
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$this->component++; |
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$this->depthFirstSearch($node, $this->component); |
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// Find the next unallocated node. |
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$node = array_search(0, $this->nodes, true); |
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} |
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return $this->groupResults(); |
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} |
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/** |
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* Group the nodes by component. |
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* |
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* @return array |
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*/ |
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private function groupResults() |
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{ |
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$result = array(); |
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foreach ($this->nodes as $node => $component) { |
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if (array_key_exists($component, $result)) { |
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$result[$component][] = $node; |
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} else { |
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$result[$component] = array($node); |
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} |
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} |
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return $result; |
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} |
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/** |
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* Find all nodes connected to $node and mark them as part of |
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* component $component. |
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* |
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* @param $node |
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* @param $component |
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*/ |
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private function depthFirstSearch($node, $component) |
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{ |
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$this->nodes[$node] = $component; |
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foreach (array_keys($this->graph[$node]) as $next) { |
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if ($this->nodes[$next] === 0) { |
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$this->depthFirstSearch($next, $component); |
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} |
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} |
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} |
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} |
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fisharebest /
algorithm
