private LinkedList<ViterbiNode> convertUnknownWordToUnigramNode(ViterbiNode node) {
LinkedList<ViterbiNode> uniGramNodes = new LinkedList<>();
int unigramWordId = 0;
String surface = node.getSurface();
for (int i = surface.length(); i > 0; i--) {
String word = surface.substring(i - 1, i);
int startIndex = node.getStartIndex() + i - 1;
ViterbiNode uniGramNode =
new ViterbiNode(
unigramWordId, word, unknownDictionary, startIndex, ViterbiNode.Type.UNKNOWN);
uniGramNodes.addFirst(uniGramNode);
}
return uniGramNodes;
}
private void updateNode(ViterbiNode[] viterbiNodes, ViterbiNode node) {
int backwardConnectionId = node.getLeftId();
int wordCost = node.getWordCost();
int leastPathCost = DEFAULT_COST;
for (ViterbiNode leftNode : viterbiNodes) {
// If array doesn't contain any more ViterbiNodes, continue to next index
if (leftNode == null) {
return;
} else {
// cost = [total cost from BOS to previous node] + [connection cost between previous node
// and current node] + [word cost]
int pathCost =
leftNode.getPathCost()
+ costs.get(leftNode.getRightId(), backwardConnectionId)
+ wordCost;
// Add extra cost for long nodes in "Search mode".
if (mode == TokenizerBase.Mode.SEARCH || mode == TokenizerBase.Mode.EXTENDED) {
pathCost += getPenaltyCost(node);
}
// If total cost is lower than before, set current previous node as best left node (previous
// means left).
if (pathCost < leastPathCost) {
leastPathCost = pathCost;
node.setPathCost(leastPathCost);
node.setLeftNode(leftNode);
}
}
}
}
private int getPenaltyCost(ViterbiNode node) {
int pathCost = 0;
String surface = node.getSurface();
int length = surface.length();
if (length > kanjiPenaltyLengthTreshold) {
if (isKanjiOnly(surface)) { // Process only Kanji keywords
pathCost += (length - kanjiPenaltyLengthTreshold) * kanjiPenalty;
} else if (length > otherPenaltyLengthThreshold) {
pathCost += (length - otherPenaltyLengthThreshold) * otherPenalty;
}
}
return pathCost;
}
private LinkedList<ViterbiNode> backtrackBestPath(ViterbiNode eos) {
ViterbiNode node = eos;
LinkedList<ViterbiNode> result = new LinkedList<>();
result.add(node);
while (true) {
ViterbiNode leftNode = node.getLeftNode();
if (leftNode == null) {
break;
} else {
// Extended mode converts unknown word into unigram nodes
if (mode == TokenizerBase.Mode.EXTENDED && leftNode.getType() == ViterbiNode.Type.UNKNOWN) {
LinkedList<ViterbiNode> uniGramNodes = convertUnknownWordToUnigramNode(leftNode);
result.addAll(uniGramNodes);
} else {
result.addFirst(leftNode);
}
node = leftNode;
}
}
return result;
}