87 lines
3.1 KiB
C++
87 lines
3.1 KiB
C++
// Copyright 2010-2024 Google LLC
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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#include "ortools/graph/assignment.h"
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#include <algorithm>
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#include <limits>
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#include "absl/flags/flag.h"
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#include "ortools/graph/ebert_graph.h"
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#include "ortools/graph/linear_assignment.h"
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namespace operations_research {
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SimpleLinearSumAssignment::SimpleLinearSumAssignment() : num_nodes_(0) {}
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ArcIndex SimpleLinearSumAssignment::AddArcWithCost(NodeIndex left_node,
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NodeIndex right_node,
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CostValue cost) {
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const ArcIndex num_arcs = arc_cost_.size();
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num_nodes_ = std::max(num_nodes_, left_node + 1);
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num_nodes_ = std::max(num_nodes_, right_node + 1);
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arc_tail_.push_back(left_node);
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arc_head_.push_back(right_node);
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arc_cost_.push_back(cost);
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return num_arcs;
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}
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NodeIndex SimpleLinearSumAssignment::NumNodes() const { return num_nodes_; }
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ArcIndex SimpleLinearSumAssignment::NumArcs() const { return arc_cost_.size(); }
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NodeIndex SimpleLinearSumAssignment::LeftNode(ArcIndex arc) const {
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return arc_tail_[arc];
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}
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NodeIndex SimpleLinearSumAssignment::RightNode(ArcIndex arc) const {
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return arc_head_[arc];
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}
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CostValue SimpleLinearSumAssignment::Cost(ArcIndex arc) const {
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return arc_cost_[arc];
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}
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SimpleLinearSumAssignment::Status SimpleLinearSumAssignment::Solve() {
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optimal_cost_ = 0;
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assignment_arcs_.clear();
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if (NumNodes() == 0) return OPTIMAL;
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// HACK(user): Detect overflows early. In ./linear_assignment.h, the cost of
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// each arc is internally multiplied by cost_scaling_factor_ (which is equal
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// to (num_nodes + 1)) without overflow checking.
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const CostValue max_supported_arc_cost =
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std::numeric_limits<CostValue>::max() / (NumNodes() + 1);
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for (const CostValue unscaled_arc_cost : arc_cost_) {
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if (unscaled_arc_cost > max_supported_arc_cost) return POSSIBLE_OVERFLOW;
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}
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const ArcIndex num_arcs = arc_cost_.size();
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ForwardStarGraph graph(2 * num_nodes_, num_arcs);
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LinearSumAssignment<ForwardStarGraph> assignment(graph, num_nodes_);
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for (ArcIndex arc = 0; arc < num_arcs; ++arc) {
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graph.AddArc(arc_tail_[arc], num_nodes_ + arc_head_[arc]);
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assignment.SetArcCost(arc, arc_cost_[arc]);
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}
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// TODO(user): Improve the LinearSumAssignment api to clearly define
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// the error cases.
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if (!assignment.FinalizeSetup()) return POSSIBLE_OVERFLOW;
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if (!assignment.ComputeAssignment()) return INFEASIBLE;
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optimal_cost_ = assignment.GetCost();
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for (NodeIndex node = 0; node < num_nodes_; ++node) {
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assignment_arcs_.push_back(assignment.GetAssignmentArc(node));
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}
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return OPTIMAL;
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}
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} // namespace operations_research
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