134 lines
4.5 KiB
C++
134 lines
4.5 KiB
C++
// Copyright 2010-2024 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 OR_TOOLS_ALGORITHMS_SPARSE_PERMUTATION_H_
|
|
#define OR_TOOLS_ALGORITHMS_SPARSE_PERMUTATION_H_
|
|
|
|
#include <string>
|
|
#include <vector>
|
|
|
|
#include "ortools/base/logging.h"
|
|
|
|
namespace operations_research {
|
|
|
|
// A compact representation for permutations of {0..N-1} that displaces few
|
|
// elements: it needs only O(K) memory for a permutation that displaces
|
|
// K elements.
|
|
class SparsePermutation {
|
|
public:
|
|
explicit SparsePermutation(int size) : size_(size) {} // Identity.
|
|
|
|
// TODO(user): complete the reader API.
|
|
int Size() const { return size_; }
|
|
int NumCycles() const { return cycle_ends_.size(); }
|
|
|
|
// Returns the "support" of this permutation; that is, the set of elements
|
|
// displaced by it.
|
|
const std::vector<int>& Support() const { return cycles_; }
|
|
|
|
// The permutation has NumCycles() cycles numbered 0 .. NumCycles()-1.
|
|
// To iterate over cycle #i of the permutation, do this:
|
|
// for (const int e : permutation.Cycle(i)) { ...
|
|
struct Iterator;
|
|
Iterator Cycle(int i) const;
|
|
|
|
// This is useful for iterating over the pair {element, image}
|
|
// of a permutation:
|
|
//
|
|
// for (int c = 0; c < perm.NumCycles(); ++c) {
|
|
// int element = LastElementInCycle(c);
|
|
// for (int image : perm.Cycle(c)) {
|
|
// // The pair is (element, image).
|
|
// ...
|
|
// element = image;
|
|
// }
|
|
// }
|
|
//
|
|
// TODO(user): Provide a full iterator for this? Note that we have more
|
|
// information with the loop above. Not sure it is needed though.
|
|
int LastElementInCycle(int i) const;
|
|
|
|
// To add a cycle to the permutation, repeatedly call AddToCurrentCycle()
|
|
// with the cycle's orbit, then call CloseCurrentCycle();
|
|
// This shouldn't be called on trivial cycles (of length 1).
|
|
void AddToCurrentCycle(int x);
|
|
void CloseCurrentCycle();
|
|
|
|
// Removes the cycles with given indices from the permutation. This
|
|
// works in O(K) for a permutation displacing K elements.
|
|
void RemoveCycles(const std::vector<int>& cycle_indices);
|
|
|
|
// Output all non-identity cycles of the permutation, sorted
|
|
// lexicographically (each cycle is described starting by its smallest
|
|
// element; and all cycles are sorted lexicographically against each other).
|
|
// This isn't efficient; use for debugging only.
|
|
// Example: "(1 4 3) (5 9) (6 8 7)".
|
|
std::string DebugString() const;
|
|
|
|
private:
|
|
const int size_;
|
|
std::vector<int> cycles_;
|
|
std::vector<int> cycle_ends_;
|
|
};
|
|
|
|
inline void SparsePermutation::AddToCurrentCycle(int x) {
|
|
DCHECK_GE(x, 0);
|
|
DCHECK_LT(x, size_);
|
|
cycles_.push_back(x);
|
|
}
|
|
|
|
inline void SparsePermutation::CloseCurrentCycle() {
|
|
if (cycle_ends_.empty()) {
|
|
DCHECK_GE(cycles_.size(), 2);
|
|
} else {
|
|
DCHECK_GE(cycles_.size(), cycle_ends_.back() + 2);
|
|
}
|
|
cycle_ends_.push_back(cycles_.size());
|
|
}
|
|
|
|
struct SparsePermutation::Iterator {
|
|
// These typedefs allow this iterator to be used within testing::ElementsAre.
|
|
typedef int value_type;
|
|
typedef std::vector<int>::const_iterator const_iterator;
|
|
|
|
Iterator() = default;
|
|
Iterator(const std::vector<int>::const_iterator& b,
|
|
const std::vector<int>::const_iterator& e)
|
|
: begin_(b), end_(e) {}
|
|
|
|
std::vector<int>::const_iterator begin() const { return begin_; }
|
|
std::vector<int>::const_iterator end() const { return end_; }
|
|
const std::vector<int>::const_iterator begin_;
|
|
const std::vector<int>::const_iterator end_;
|
|
|
|
int size() const { return end_ - begin_; }
|
|
};
|
|
|
|
inline SparsePermutation::Iterator SparsePermutation::Cycle(int i) const {
|
|
DCHECK_GE(i, 0);
|
|
DCHECK_LT(i, NumCycles());
|
|
return Iterator(cycles_.begin() + (i == 0 ? 0 : cycle_ends_[i - 1]),
|
|
cycles_.begin() + cycle_ends_[i]);
|
|
}
|
|
|
|
inline int SparsePermutation::LastElementInCycle(int i) const {
|
|
DCHECK_GE(i, 0);
|
|
DCHECK_LT(i, cycle_ends_.size());
|
|
DCHECK_GT(cycle_ends_[i], i == 0 ? 0 : cycle_ends_[i - 1]);
|
|
return cycles_[cycle_ends_[i] - 1];
|
|
}
|
|
|
|
} // namespace operations_research
|
|
|
|
#endif // OR_TOOLS_ALGORITHMS_SPARSE_PERMUTATION_H_
|