Permutations<T> constructor

Permutations<T>(
  1. int r,
  2. List<T> items
)

Implementation

Permutations(this.r, List<T> items)
    : _items = List<T>.from(items, growable: false),
      _length = nPr(items.length, r) {
  if (r < 0 || r > items.length) {
    throw Exception("Cannot take $r items from ${items.length}.");
  }
  if (!itemsAreUnique(items)) {
    throw Exception("Items are not unique.");
  }
}