chooseCached function
Implementation
int chooseCached(int n, int r) {
if (!_chooseCache.containsKey(n)) {
_chooseCache[n] = {};
}
if (!(_chooseCache[n])!.containsKey(r)) {
_chooseCache[n]![r] = choose(n, r, useCache: false);
}
return _chooseCache[n]![r]!;
}