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ortools-clone/ortools/sat/diffn_util.cc

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// Copyright 2010-2022 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.
#include "ortools/sat/diffn_util.h"
#include <stddef.h>
#include <algorithm>
#include <ostream>
#include <utility>
#include <vector>
#include "absl/container/flat_hash_set.h"
#include "absl/log/check.h"
#include "absl/random/bit_gen_ref.h"
#include "absl/types/span.h"
#include "ortools/base/logging.h"
#include "ortools/base/stl_util.h"
#include "ortools/sat/integer.h"
#include "ortools/sat/intervals.h"
#include "ortools/util/integer_pq.h"
#include "ortools/util/strong_integers.h"
namespace operations_research {
namespace sat {
bool Rectangle::IsDisjoint(const Rectangle& other) const {
return x_min >= other.x_max || other.x_min >= x_max || y_min >= other.y_max ||
other.y_min >= y_max;
}
std::vector<absl::Span<int>> GetOverlappingRectangleComponents(
const std::vector<Rectangle>& rectangles,
absl::Span<int> active_rectangles) {
if (active_rectangles.empty()) return {};
std::vector<absl::Span<int>> result;
const int size = active_rectangles.size();
for (int start = 0; start < size;) {
// Find the component of active_rectangles[start].
int end = start + 1;
for (int i = start; i < end; i++) {
for (int j = end; j < size; ++j) {
if (!rectangles[active_rectangles[i]].IsDisjoint(
rectangles[active_rectangles[j]])) {
std::swap(active_rectangles[end++], active_rectangles[j]);
}
}
}
if (end > start + 1) {
result.push_back(active_rectangles.subspan(start, end - start));
}
start = end;
}
return result;
}
bool ReportEnergyConflict(Rectangle bounding_box, absl::Span<const int> boxes,
SchedulingConstraintHelper* x,
SchedulingConstraintHelper* y) {
x->ClearReason();
y->ClearReason();
IntegerValue total_energy(0);
for (const int b : boxes) {
const IntegerValue x_min = x->ShiftedStartMin(b);
const IntegerValue x_max = x->ShiftedEndMax(b);
if (x_min < bounding_box.x_min || x_max > bounding_box.x_max) continue;
const IntegerValue y_min = y->ShiftedStartMin(b);
const IntegerValue y_max = y->ShiftedEndMax(b);
if (y_min < bounding_box.y_min || y_max > bounding_box.y_max) continue;
x->AddEnergyMinInIntervalReason(b, bounding_box.x_min, bounding_box.x_max);
y->AddEnergyMinInIntervalReason(b, bounding_box.y_min, bounding_box.y_max);
x->AddPresenceReason(b);
y->AddPresenceReason(b);
total_energy += x->SizeMin(b) * y->SizeMin(b);
// We abort early if a subset of boxes is enough.
// TODO(user): Also relax the box if possible.
if (total_energy > bounding_box.Area()) break;
}
CHECK_GT(total_energy, bounding_box.Area());
x->ImportOtherReasons(*y);
return x->ReportConflict();
}
bool BoxesAreInEnergyConflict(const std::vector<Rectangle>& rectangles,
const std::vector<IntegerValue>& energies,
absl::Span<const int> boxes,
Rectangle* conflict) {
// First consider all relevant intervals along the x axis.
std::vector<IntegerValue> x_starts;
std::vector<TaskTime> boxes_by_increasing_x_max;
for (const int b : boxes) {
x_starts.push_back(rectangles[b].x_min);
boxes_by_increasing_x_max.push_back({b, rectangles[b].x_max});
}
gtl::STLSortAndRemoveDuplicates(&x_starts);
std::sort(boxes_by_increasing_x_max.begin(), boxes_by_increasing_x_max.end());
std::vector<IntegerValue> y_starts;
std::vector<IntegerValue> energy_sum;
std::vector<TaskTime> boxes_by_increasing_y_max;
std::vector<std::vector<int>> stripes(x_starts.size());
for (int i = 0; i < boxes_by_increasing_x_max.size(); ++i) {
const int b = boxes_by_increasing_x_max[i].task_index;
const IntegerValue x_min = rectangles[b].x_min;
const IntegerValue x_max = rectangles[b].x_max;
for (int j = 0; j < x_starts.size(); ++j) {
if (x_starts[j] > x_min) break;
stripes[j].push_back(b);
// Redo the same on the y coordinate for the current x interval
// which is [starts[j], x_max].
y_starts.clear();
boxes_by_increasing_y_max.clear();
for (const int b : stripes[j]) {
y_starts.push_back(rectangles[b].y_min);
boxes_by_increasing_y_max.push_back({b, rectangles[b].y_max});
}
gtl::STLSortAndRemoveDuplicates(&y_starts);
std::sort(boxes_by_increasing_y_max.begin(),
boxes_by_increasing_y_max.end());
const IntegerValue x_size = x_max - x_starts[j];
energy_sum.assign(y_starts.size(), IntegerValue(0));
for (int i = 0; i < boxes_by_increasing_y_max.size(); ++i) {
const int b = boxes_by_increasing_y_max[i].task_index;
const IntegerValue y_min = rectangles[b].y_min;
const IntegerValue y_max = rectangles[b].y_max;
for (int j = 0; j < y_starts.size(); ++j) {
if (y_starts[j] > y_min) break;
energy_sum[j] += energies[b];
if (energy_sum[j] > x_size * (y_max - y_starts[j])) {
if (conflict != nullptr) {
*conflict = rectangles[b];
for (int k = 0; k < i; ++k) {
const int task_index = boxes_by_increasing_y_max[k].task_index;
if (rectangles[task_index].y_min >= y_starts[j]) {
conflict->TakeUnionWith(rectangles[task_index]);
}
}
}
return true;
}
}
}
}
}
return false;
}
bool AnalyzeIntervals(bool transpose, absl::Span<const int> local_boxes,
const std::vector<Rectangle>& rectangles,
const std::vector<IntegerValue>& rectangle_energies,
IntegerValue* x_threshold, IntegerValue* y_threshold,
Rectangle* conflict) {
// First, we compute the possible x_min values (removing duplicates).
// We also sort the relevant tasks by their x_max.
//
// TODO(user): If the number of unique x_max is smaller than the number of
// unique x_min, it is better to do it the other way around.
std::vector<IntegerValue> starts;
std::vector<TaskTime> task_by_increasing_x_max;
for (const int t : local_boxes) {
const IntegerValue x_min =
transpose ? rectangles[t].y_min : rectangles[t].x_min;
const IntegerValue x_max =
transpose ? rectangles[t].y_max : rectangles[t].x_max;
starts.push_back(x_min);
task_by_increasing_x_max.push_back({t, x_max});
}
gtl::STLSortAndRemoveDuplicates(&starts);
// Note that for the same end_max, the order change our heuristic to
// evaluate the max_conflict_height.
std::sort(task_by_increasing_x_max.begin(), task_by_increasing_x_max.end());
// The maximum y dimension of a bounding area for which there is a potential
// conflict.
IntegerValue max_conflict_height(0);
// This is currently only used for logging.
absl::flat_hash_set<std::pair<IntegerValue, IntegerValue>> stripes;
// All quantities at index j correspond to the interval [starts[j], x_max].
std::vector<IntegerValue> energies(starts.size(), IntegerValue(0));
std::vector<IntegerValue> y_mins(starts.size(), kMaxIntegerValue);
std::vector<IntegerValue> y_maxs(starts.size(), -kMaxIntegerValue);
std::vector<IntegerValue> energy_at_max_y(starts.size(), IntegerValue(0));
std::vector<IntegerValue> energy_at_min_y(starts.size(), IntegerValue(0));
// Sentinel.
starts.push_back(kMaxIntegerValue);
// Iterate over all boxes by increasing x_max values.
int first_j = 0;
const IntegerValue threshold = transpose ? *y_threshold : *x_threshold;
for (int i = 0; i < task_by_increasing_x_max.size(); ++i) {
const int t = task_by_increasing_x_max[i].task_index;
const IntegerValue energy = rectangle_energies[t];
IntegerValue x_min = rectangles[t].x_min;
IntegerValue x_max = rectangles[t].x_max;
IntegerValue y_min = rectangles[t].y_min;
IntegerValue y_max = rectangles[t].y_max;
if (transpose) {
std::swap(x_min, y_min);
std::swap(x_max, y_max);
}
// Add this box contribution to all the [starts[j], x_max] intervals.
while (first_j + 1 < starts.size() && x_max - starts[first_j] > threshold) {
++first_j;
}
for (int j = first_j; starts[j] <= x_min; ++j) {
const IntegerValue old_energy_at_max = energy_at_max_y[j];
const IntegerValue old_energy_at_min = energy_at_min_y[j];
energies[j] += energy;
const bool is_disjoint = y_min >= y_maxs[j] || y_max <= y_mins[j];
if (y_min <= y_mins[j]) {
if (y_min < y_mins[j]) {
y_mins[j] = y_min;
energy_at_min_y[j] = energy;
} else {
energy_at_min_y[j] += energy;
}
}
if (y_max >= y_maxs[j]) {
if (y_max > y_maxs[j]) {
y_maxs[j] = y_max;
energy_at_max_y[j] = energy;
} else {
energy_at_max_y[j] += energy;
}
}
// If the new box is disjoint in y from the ones added so far, there
// cannot be a new conflict involving this box, so we skip until we add
// new boxes.
if (is_disjoint) continue;
const IntegerValue width = x_max - starts[j];
IntegerValue conflict_height = CeilRatio(energies[j], width) - 1;
if (y_max - y_min > conflict_height) continue;
if (conflict_height >= y_maxs[j] - y_mins[j]) {
// We have a conflict.
if (conflict != nullptr) {
*conflict = rectangles[t];
for (int k = 0; k < i; ++k) {
const int task_index = task_by_increasing_x_max[k].task_index;
const IntegerValue task_x_min = transpose
? rectangles[task_index].y_min
: rectangles[task_index].x_min;
if (task_x_min < starts[j]) continue;
conflict->TakeUnionWith(rectangles[task_index]);
}
}
return false;
}
// Because we currently do not have a conflict involving the new box, the
// only way to have one is to remove enough energy to reduce the y domain.
IntegerValue can_remove = std::min(old_energy_at_min, old_energy_at_max);
if (old_energy_at_min < old_energy_at_max) {
if (y_maxs[j] - y_min >=
CeilRatio(energies[j] - old_energy_at_min, width)) {
// In this case, we need to remove at least old_energy_at_max to have
// a conflict.
can_remove = old_energy_at_max;
}
} else if (old_energy_at_max < old_energy_at_min) {
if (y_max - y_mins[j] >=
CeilRatio(energies[j] - old_energy_at_max, width)) {
can_remove = old_energy_at_min;
}
}
conflict_height = CeilRatio(energies[j] - can_remove, width) - 1;
// If the new box height is above the conflict_height, do not count
// it now. We only need to consider conflict involving the new box.
if (y_max - y_min > conflict_height) continue;
if (VLOG_IS_ON(2)) stripes.insert({starts[j], x_max});
max_conflict_height = std::max(max_conflict_height, conflict_height);
}
}
VLOG(2) << " num_starts: " << starts.size() - 1 << "/" << local_boxes.size()
<< " conflict_height: " << max_conflict_height
<< " num_stripes:" << stripes.size() << " (<= " << threshold << ")";
if (transpose) {
*x_threshold = std::min(*x_threshold, max_conflict_height);
} else {
*y_threshold = std::min(*y_threshold, max_conflict_height);
}
return true;
}
absl::Span<int> FilterBoxesAndRandomize(
const std::vector<Rectangle>& cached_rectangles, absl::Span<int> boxes,
IntegerValue threshold_x, IntegerValue threshold_y,
absl::BitGenRef random) {
size_t new_size = 0;
for (const int b : boxes) {
const Rectangle& dim = cached_rectangles[b];
if (dim.x_max - dim.x_min > threshold_x) continue;
if (dim.y_max - dim.y_min > threshold_y) continue;
boxes[new_size++] = b;
}
if (new_size == 0) return {};
std::shuffle(&boxes[0], &boxes[0] + new_size, random);
return {&boxes[0], new_size};
}
absl::Span<int> FilterBoxesThatAreTooLarge(
const std::vector<Rectangle>& cached_rectangles,
const std::vector<IntegerValue>& energies, absl::Span<int> boxes) {
// Sort the boxes by increasing area.
std::sort(boxes.begin(), boxes.end(), [&cached_rectangles](int a, int b) {
return cached_rectangles[a].Area() < cached_rectangles[b].Area();
});
IntegerValue total_energy(0);
for (const int box : boxes) total_energy += energies[box];
// Remove all the large boxes until we have one with area smaller than the
// energy of the boxes below.
int new_size = boxes.size();
while (new_size > 0 &&
cached_rectangles[boxes[new_size - 1]].Area() >= total_energy) {
--new_size;
total_energy -= energies[boxes[new_size]];
}
return boxes.subspan(0, new_size);
}
std::ostream& operator<<(std::ostream& out, const IndexedInterval& interval) {
return out << "[" << interval.start << ".." << interval.end << " (#"
<< interval.index << ")]";
}
void ConstructOverlappingSets(bool already_sorted,
std::vector<IndexedInterval>* intervals,
std::vector<std::vector<int>>* result) {
result->clear();
if (already_sorted) {
DCHECK(std::is_sorted(intervals->begin(), intervals->end(),
IndexedInterval::ComparatorByStart()));
} else {
std::sort(intervals->begin(), intervals->end(),
IndexedInterval::ComparatorByStart());
}
IntegerValue min_end_in_set = kMaxIntegerValue;
intervals->push_back({-1, kMaxIntegerValue, kMaxIntegerValue}); // Sentinel.
const int size = intervals->size();
// We do a line sweep. The "current" subset crossing the "line" at
// (time, time + 1) will be in (*intervals)[start_index, end_index) at the end
// of the loop block.
int start_index = 0;
for (int end_index = 0; end_index < size;) {
const IntegerValue time = (*intervals)[end_index].start;
// First, if there is some deletion, we will push the "old" set to the
// result before updating it. Otherwise, we will have a superset later, so
// we just continue for now.
if (min_end_in_set <= time) {
result->push_back({});
min_end_in_set = kMaxIntegerValue;
for (int i = start_index; i < end_index; ++i) {
result->back().push_back((*intervals)[i].index);
if ((*intervals)[i].end <= time) {
std::swap((*intervals)[start_index++], (*intervals)[i]);
} else {
min_end_in_set = std::min(min_end_in_set, (*intervals)[i].end);
}
}
// Do not output subset of size one.
if (result->back().size() == 1) result->pop_back();
}
// Add all the new intervals starting exactly at "time".
do {
min_end_in_set = std::min(min_end_in_set, (*intervals)[end_index].end);
++end_index;
} while (end_index < size && (*intervals)[end_index].start == time);
}
}
void GetOverlappingIntervalComponents(
std::vector<IndexedInterval>* intervals,
std::vector<std::vector<int>>* components) {
components->clear();
if (intervals->empty()) return;
if (intervals->size() == 1) {
components->push_back({intervals->front().index});
return;
}
// For correctness, ComparatorByStart is enough, but in unit tests we want to
// verify this function against another implementation, and fully defined
// sorting with tie-breaking makes that much easier.
// If that becomes a performance bottleneck:
// - One may want to sort the list outside of this function, and simply
// have this function DCHECK that it's sorted by start.
// - One may use stable_sort() with ComparatorByStart().
std::sort(intervals->begin(), intervals->end(),
IndexedInterval::ComparatorByStartThenEndThenIndex());
IntegerValue end_max_so_far = (*intervals)[0].end;
components->push_back({(*intervals)[0].index});
for (int i = 1; i < intervals->size(); ++i) {
const IndexedInterval& interval = (*intervals)[i];
if (interval.start >= end_max_so_far) {
components->push_back({interval.index});
} else {
components->back().push_back(interval.index);
}
end_max_so_far = std::max(end_max_so_far, interval.end);
}
}
std::vector<int> GetIntervalArticulationPoints(
std::vector<IndexedInterval>* intervals) {
std::vector<int> articulation_points;
if (intervals->size() < 3) return articulation_points; // Empty.
if (DEBUG_MODE) {
for (const IndexedInterval& interval : *intervals) {
DCHECK_LT(interval.start, interval.end);
}
}
std::sort(intervals->begin(), intervals->end(),
IndexedInterval::ComparatorByStart());
IntegerValue end_max_so_far = (*intervals)[0].end;
int index_of_max = 0;
IntegerValue prev_end_max = kMinIntegerValue; // Initialized as a sentinel.
for (int i = 1; i < intervals->size(); ++i) {
const IndexedInterval& interval = (*intervals)[i];
if (interval.start >= end_max_so_far) {
// New connected component.
end_max_so_far = interval.end;
index_of_max = i;
prev_end_max = kMinIntegerValue;
continue;
}
// Still the same connected component. Was the previous "max" an
// articulation point ?
if (prev_end_max != kMinIntegerValue && interval.start >= prev_end_max) {
// We might be re-inserting the same articulation point: guard against it.
if (articulation_points.empty() ||
articulation_points.back() != index_of_max) {
articulation_points.push_back(index_of_max);
}
}
// Update the max end.
if (interval.end > end_max_so_far) {
prev_end_max = end_max_so_far;
end_max_so_far = interval.end;
index_of_max = i;
} else if (interval.end > prev_end_max) {
prev_end_max = interval.end;
}
}
// Convert articulation point indices to IndexedInterval.index.
for (int& index : articulation_points) index = (*intervals)[index].index;
return articulation_points;
}
void CapacityProfile::Clear() {
events_.clear();
num_rectangles_added_ = 0;
}
void CapacityProfile::AddRectangle(IntegerValue x_min, IntegerValue x_max,
IntegerValue y_min, IntegerValue y_max) {
DCHECK_LE(x_min, x_max);
if (x_min == x_max) return;
events_.push_back(
StartRectangleEvent(num_rectangles_added_, x_min, y_min, y_max));
events_.push_back(EndRectangleEvent(num_rectangles_added_, x_max));
++num_rectangles_added_;
}
void CapacityProfile::AddMandatoryConsumption(IntegerValue x_min,
IntegerValue x_max,
IntegerValue y_height) {
DCHECK_LE(x_min, x_max);
if (x_min == x_max) return;
events_.push_back(ChangeMandatoryProfileEvent(x_min, y_height));
events_.push_back(ChangeMandatoryProfileEvent(x_max, -y_height));
}
void CapacityProfile::BuildResidualCapacityProfile(
std::vector<CapacityProfile::Rectangle>* result) {
std::sort(events_.begin(), events_.end());
IntegerPriorityQueue<QueueElement> min_pq(num_rectangles_added_);
IntegerPriorityQueue<QueueElement> max_pq(num_rectangles_added_);
IntegerValue mandatory_capacity(0);
result->clear();
result->push_back({kMinIntegerValue, IntegerValue(0)});
for (int i = 0; i < events_.size();) {
const IntegerValue current_time = events_[i].time;
for (; i < events_.size(); ++i) {
const Event& event = events_[i];
if (event.time != current_time) break;
switch (events_[i].type) {
case START_RECTANGLE: {
min_pq.Add({event.index, -event.y_min});
max_pq.Add({event.index, event.y_max});
break;
}
case END_RECTANGLE: {
min_pq.Remove(event.index);
max_pq.Remove(event.index);
break;
}
case CHANGE_MANDATORY_PROFILE: {
mandatory_capacity += event.y_min;
break;
}
}
}
DCHECK(!max_pq.IsEmpty() || mandatory_capacity == 0);
const IntegerValue new_height =
max_pq.IsEmpty()
? IntegerValue(0)
: max_pq.Top().value + min_pq.Top().value - mandatory_capacity;
if (new_height != result->back().height) {
result->push_back({current_time, new_height});
}
}
}
IntegerValue CapacityProfile::GetBoundingArea() {
std::sort(events_.begin(), events_.end());
IntegerPriorityQueue<QueueElement> min_pq(num_rectangles_added_);
IntegerPriorityQueue<QueueElement> max_pq(num_rectangles_added_);
IntegerValue area(0);
IntegerValue previous_time = kMinIntegerValue;
IntegerValue previous_height(0);
for (int i = 0; i < events_.size();) {
const IntegerValue current_time = events_[i].time;
for (; i < events_.size(); ++i) {
const Event& event = events_[i];
if (event.time != current_time) break;
switch (event.type) {
case START_RECTANGLE: {
min_pq.Add({event.index, -event.y_min});
max_pq.Add({event.index, event.y_max});
break;
}
case END_RECTANGLE: {
min_pq.Remove(event.index);
max_pq.Remove(event.index);
break;
}
case CHANGE_MANDATORY_PROFILE: {
break;
}
}
}
const IntegerValue new_height =
max_pq.IsEmpty() ? IntegerValue(0)
: max_pq.Top().value + min_pq.Top().value;
if (previous_height != 0) {
area += previous_height * (current_time - previous_time);
}
previous_time = current_time;
previous_height = new_height;
}
return area;
}
} // namespace sat
} // namespace operations_research