public static long binomial(LongPair pair) {
Object find = pascal.get(pair);
if (find == null) {
long l = binomial(pair.x() - 1, pair.y() - 1);
long r = binomial(pair.x() - 1, pair.y());
pascal.put(pair, new Long(l + r));
return l + r;
}
return ((Long) find).longValue();
}
