| // Copyright 2016 Google Inc. All rights reserved. |
| // |
| // 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 SRC_WEIGHTED_RESERVOIR_SAMPLER_H_ |
| #define SRC_WEIGHTED_RESERVOIR_SAMPLER_H_ |
| |
| #include <cassert> |
| #include <random> |
| |
| namespace protobuf_mutator { |
| |
| // Algorithm pick one item from the sequence of weighted items. |
| // https://en.wikipedia.org/wiki/Reservoir_sampling#Algorithm_A-Chao |
| // |
| // Example: |
| // WeightedReservoirSampler<int> sampler; |
| // for(int i = 0; i < size; ++i) |
| // sampler.Pick(weight[i], i); |
| // return sampler.GetSelected(); |
| template <class T, class RandomEngine = std::default_random_engine> |
| class WeightedReservoirSampler { |
| public: |
| explicit WeightedReservoirSampler(RandomEngine* random) : random_(random) {} |
| |
| void Try(uint64_t weight, const T& item) { |
| if (Pick(weight)) selected_ = item; |
| } |
| |
| const T& selected() const { return selected_; } |
| |
| bool IsEmpty() const { return total_weight_ == 0; } |
| |
| private: |
| bool Pick(uint64_t weight) { |
| if (weight == 0) return false; |
| total_weight_ += weight; |
| return weight == total_weight_ || std::uniform_int_distribution<uint64_t>( |
| 1, total_weight_)(*random_) <= weight; |
| } |
| |
| T selected_ = {}; |
| uint64_t total_weight_ = 0; |
| RandomEngine* random_; |
| }; |
| |
| } // namespace protobuf_mutator |
| |
| #endif // SRC_WEIGHTED_RESERVOIR_SAMPLER_H_ |