/** Dijkstra Algorithm for searching of the shortest path between words $first and $finish
* https://en.wikipedia.org/wiki/Dijkstra's_algorithm
*
* Gets shortest paths from a word with ID $first to $finish,
* writes shortest path (distance and path) to arrays while $finish is not marked.
*
* @param int $first a first word in a shortest path
* @param int $finish a last word in a shortest path
*/
public static function DijkstraAlgorithmByArray($first, $finish)
{
global $LINK_DB;
if ($first == $finish) {
return array(0, array($first));
}
$vertex_arr = PWRelatedWords::getAllRelatedWords();
// list of unvisited vertexes generated from list of vertexes having an edge
if (!in_array($first, $vertex_arr)) {
return array(0, NULL);
}
// search vertexes is not connected with any edge
$infinity = 1000000;
foreach ($vertex_arr as $v) {
$unvisited[$v] = $infinity;
}
$unvisited[$first] = 0;
$edge_table = PWRelatedWords::getTableName();
// table of related words (words and distance between them)
$prev_arr = array();
// list of next-to-last for path from first to last vertexes
$prev_arr[$first] = NULL;
$prev = $first;
$path_len = 0;
// $dist_arr = array(); // <key>,<value>: list of distances <value> from $first to <key>
// $dist_arr[$first] =0;
$success = 0;
// the condition of finding the shortest path in the given vertex ($finish)
//print "<PRE>";
$count = 0;
//print $first;
//return;
while (!$success && sizeof($unvisited) && $path_len < $infinity) {
// until all vertixes will not be visited
// && $count<10
print "<p>" . $count . ": " . sizeof($unvisited);
//.".-----------------------------</p>";
//print_r($finish_arr);
//print_r($len_arr);
$query = "SELECT * FROM {$edge_table} WHERE lemma_id1='{$prev}' or lemma_id2='{$prev}'";
// search nearest vertexes to $prev (НЕТ необходимости сортировать, так как неважно в какой последовательности ставятся метки)
$res_neib = $LINK_DB->query_e($query, "Query failed in file <b>" . __FILE__ . "</b>, string <b>" . __LINE__ . "</b>");
while ($row_neib = $res_neib->fetch_object()) {
if ($row_neib->lemma_id1 == $prev) {
$last = $row_neib->lemma_id2;
} else {
$last = $row_neib->lemma_id1;
}
$new_path_len = $path_len + $row_neib->weight;
// path length from $prev to $last (neighbour of $prev via semantic relations)
// if (!isset($dist_arr[$last]) || $dist_arr[$last]>$new_path_len) { // this is new path from $first to $last OR
if (isset($unvisited[$last]) && $unvisited[$last] > $new_path_len) {
// this is new path from $first to $last OR
// already (one) path from $first to $last does exist, but the new path is shorter
// $dist_arr[$last] =
$unvisited[$last] = $new_path_len;
$prev_arr[$last] = $prev;
}
}
$count++;
$path_len = min(array_values($unvisited));
// choose minimal distance of path from first to any unvisited vertex
$prev = array_search($path_len, $unvisited);
// choose unvisited vertex with minimal distance
print " = " . $path_len;
unset($unvisited[$prev]);
// mark this vertes as visited, delete it from unvisited list
if ($prev == $finish) {
// the shortest path in $finish are found!!
$success = 1;
continue;
}
}
print "<p>{$count} iterations";
if ($success) {
//
$path = array($finish);
$prev = $prev_arr[$finish];
while ($prev != NULL) {
array_unshift($path, $prev);
$prev = $prev_arr[$prev];
}
return array($path_len, $path);
} else {
return array(NULL, NULL);
}
// any path from $first to $finish are not found
}
