/**
* Finds the first or last occurrence of a phrase in the suffix array, within a subset of the
* suffix array that is bounded by suffixArrayStart and suffixArrayEnd. For efficiency of looking
* up all subphrases in a sentence we do not require that multplie int[]s be created for each
* subphrase. Instead this method will look for the subphrase within the sentence between
* phraseStart and phraseEnd.
*
* @param sentence the sentence/superphrase in int representation to draw the search phrase from
* @param phraseStart the start of the phrase in the sentence (inclusive)
* @param phraseEnd the end of the phrase in the sentence (exclusive)
* @param suffixArrayStart the point at which to start the search in the suffix array
* @param suffixArrayEnd the end point in the suffix array beyond which the search doesn't need to
* take place
* @param findFirst a flag that indicates whether we should find the first or last occurrence of
* the phrase
*/
private int findPhraseBound(
Phrase sentence,
int phraseStart,
int phraseEnd,
int suffixArrayStart,
int suffixArrayEnd,
boolean findFirst) {
int low = suffixArrayStart;
int high = suffixArrayEnd;
// Do a binary search between the low and high points
while (low <= high) {
int mid = (low + high) >> 1;
int start = suffixes[mid];
int diff = corpus.comparePhrase(start, sentence, phraseStart, phraseEnd);
if (diff == 0) {
// If the difference between the search phrase and the phrase in the corpus
// is 0, then we have found it. However, there might be multiple matches in
// the corpus, so we need to continue searching until we find the end point
int neighbor = mid;
if (findFirst) {
neighbor--;
} else {
neighbor++;
}
if (neighbor >= suffixArrayStart && neighbor <= suffixArrayEnd) {
int nextDiff = corpus.comparePhrase(suffixes[neighbor], sentence, phraseStart, phraseEnd);
if (nextDiff == 0) {
// There's another equivalent phrase, so we need to specify
// in which direction to continue searching
if (findFirst) diff = 1; // search lower
else diff = -1; // search higher
}
}
}
if (diff < 0) {
low = mid + 1;
} else if (diff > 0) {
high = mid - 1;
} else {
return mid; // this is the edge
}
}
return -1; // key not found.
}
