36 lines
1.4 KiB
C++
36 lines
1.4 KiB
C++
// Copyright 2010-2025 Google LLC
|
|
// Licensed under the Apache License, Version 2.0 (the "License");
|
|
// you may not use this file except in compliance with the License.
|
|
// You may obtain a copy of the License at
|
|
//
|
|
// http://www.apache.org/licenses/LICENSE-2.0
|
|
//
|
|
// Unless required by applicable law or agreed to in writing, software
|
|
// distributed under the License is distributed on an "AS IS" BASIS,
|
|
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
|
|
// See the License for the specific language governing permissions and
|
|
// limitations under the License.
|
|
|
|
#ifndef ORTOOLS_ALGORITHMS_N_CHOOSE_K_H_
|
|
#define ORTOOLS_ALGORITHMS_N_CHOOSE_K_H_
|
|
|
|
#include <cstdint>
|
|
|
|
#include "absl/status/statusor.h"
|
|
|
|
namespace operations_research {
|
|
// Returns the number of ways to choose k elements among n, ignoring the order,
|
|
// i.e., the binomial coefficient (n, k).
|
|
// This is like std::exp(MathUtil::LogCombinations(n, k)), but faster, with
|
|
// perfect accuracy, and returning an error iff the result would overflow an
|
|
// int64_t or if an argument is invalid (i.e., n < 0, k < 0). Returns 0 for k >
|
|
// n.
|
|
//
|
|
// NOTE(user): If you need a variation of this, ask the authors: it's very easy
|
|
// to add. E.g., other int types, other behaviors (e.g., return
|
|
// std::numeric_limits<int64_t>::max() on overflow, etc).
|
|
absl::StatusOr<int64_t> NChooseK(int64_t n, int64_t k);
|
|
} // namespace operations_research
|
|
|
|
#endif // ORTOOLS_ALGORITHMS_N_CHOOSE_K_H_
|