ortools-clone/ortools/sat/variable_expand.h

// 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_SAT_VARIABLE_EXPAND_H_
#define ORTOOLS_SAT_VARIABLE_EXPAND_H_

#include <cstdint>
#include <vector>

#include "absl/container/btree_map.h"
#include "absl/container/flat_hash_set.h"
#include "ortools/sat/presolve_context.h"
#include "ortools/sat/solution_crush.h"
#include "ortools/util/sorted_interval_list.h"

namespace operations_research {
namespace sat {

class ValueEncoding {
 public:
  ValueEncoding(int var, PresolveContext* context);
  // Build the set of observed values. This cannot be called after
  // CanonicalizeEncodedValuesAndAddEscapeValues() has been called.
  void AddValueToEncode(int64_t value);

  // This method is called after all values from lit => var ==/!= value have
  // been added. It canonicalizes the encoded values and adds an escape value
  // if needed. It there is an objective, the escape value is the min or the max
  // of the residual domain of the variable depending on the objective
  // coefficient of the variable. It there are no objective, the escape value is
  // the smallest value of the residual domain.
  // With this escape value, we can safely reduce the domain of the variable to
  // observed + escape values, and add an exactly_one constraint on all the
  // literals involved.
  void CanonicalizeEncodedValuesAndAddEscapeValue(
      bool var_in_objective, bool var_has_positive_objective_coefficient);

  // Getters on the observed values.
  bool empty() const;
  bool is_fully_encoded() const;
  const std::vector<int64_t>& encoded_values() const;

  // Setters and getters on the value encoding.
  void ForceFullEncoding();
  void CreateAllValueEncodingLiterals();
  int literal(int64_t value) const;
  const absl::btree_map<int64_t, int>& encoding() const;

 private:
  const int var_;
  const Domain var_domain_;
  PresolveContext* context_;
  std::vector<int64_t> encoded_values_;
  absl::btree_map<int64_t, int> encoding_;
  bool is_closed_ = false;
  bool is_fully_encoded_ = false;
};

class OrderEncoding {
 public:
  OrderEncoding(int var, PresolveContext* context,
                SolutionCrush& solution_crush);
  void InsertLeLiteral(int64_t value, int literal);
  void InsertGeLiteral(int64_t value, int literal);
  void CreateAllOrderEncodingLiterals(const ValueEncoding& values);
  int ge_literal(int64_t value) const;
  int le_literal(int64_t value) const;
  int num_encoded_values() const;

 private:
  void CollectAllOrderEncodingValues();

  const int var_;
  const Domain var_domain_;
  PresolveContext* context_;
  SolutionCrush& solution_crush_;
  absl::btree_map<int64_t, absl::flat_hash_set<int>> tmp_ge_to_literals_;
  absl::btree_map<int64_t, absl::flat_hash_set<int>> tmp_le_to_literals_;
  absl::btree_map<int64_t, int> encoded_le_literal_;
};

void TryToReplaceVariableByItsEncoding(int var, PresolveContext* context,
                                       SolutionCrush& solution_crush);

}  // namespace sat
}  // namespace operations_research

#endif  // ORTOOLS_SAT_VARIABLE_EXPAND_H_