/**
* Method creates node
* @param $string
* @param $left
*
* @return array|null
*/
public function createNode($string, $left)
{
if ($string == null || $string == '') {
return null;
}
$alphabet = WaveletTree::getAlphabet($string);
$isLeaf = false;
if (count($alphabet) == 1 || count($alphabet) == 2) {
$isLeaf = true;
}
$letters = array_keys($alphabet);
usort($letters, "WaveletTree::sortLetters");
//set half of letters to 0 half to 1
$dictionary = [];
for ($i = 0; $i < count($letters) / 2; $i++) {
$dictionary[$letters[$i]] = 0;
}
for ($i = count($letters) / 2; $i < count($letters); $i++) {
$dictionary[$letters[$i]] = 1;
}
$result = [];
for ($i = 0; $i < strlen($string); $i++) {
$result[$i] = $dictionary[$string[$i]];
}
//translate dictionary to node strings
return [new Node($result, $isLeaf, $left, $left + count($dictionary) - 1), $dictionary];
}
