78 lines
2.9 KiB
C++
78 lines
2.9 KiB
C++
// Copyright 2018 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/min_cost_flow.h"
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#include "ortools/base/logging.h"
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namespace operations_research {
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struct Arc {
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std::pair<NodeIndex, NodeIndex> nodes;
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FlowQuantity capacity;
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FlowQuantity unit_cost;
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};
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void SolveMinCostFlow() {
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// Define supply of each node.
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const std::vector<std::pair<NodeIndex, FlowQuantity> > supplies = {
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{ 0, 20 }, { 1, 0 }, { 2, 0 }, { 3, -5 }, { 4, -15 }
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};
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// Define each arc
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// Can't use std::tuple<NodeIndex, NodeIndex, FlowQuantity>
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// Initialization list is not working on std:tuple cf. N4387
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// Arc are stored as {{begin_node, end_node}, capacity}
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const std::vector<Arc> arcs = { { { 0, 1 }, 15, 4 }, { { 0, 2 }, 8, 4 },
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{ { 1, 2 }, 20, 2 }, { { 1, 3 }, 4, 2 },
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{ { 1, 4 }, 10, 6 }, { { 2, 3 }, 15, 1 },
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{ { 2, 4 }, 4, 3 }, { { 3, 4 }, 20, 2 },
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{ { 4, 2 }, 5, 3 } };
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StarGraph graph(supplies.size(), arcs.size());
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MinCostFlow min_cost_flow(&graph);
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for (const auto &it : arcs) {
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ArcIndex arc = graph.AddArc(it.nodes.first, it.nodes.second);
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min_cost_flow.SetArcCapacity(arc, it.capacity);
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min_cost_flow.SetArcUnitCost(arc, it.unit_cost);
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}
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for (const auto &it : supplies) {
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min_cost_flow.SetNodeSupply(it.first, it.second);
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}
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LOG(INFO) << "Solving min cost flow with: " << graph.num_nodes()
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<< " nodes, and " << graph.num_arcs() << " arcs.";
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// Find the maximum flow between node 0 and node 4.
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min_cost_flow.Solve();
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if (MinCostFlow::OPTIMAL != min_cost_flow.status()) {
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LOG(FATAL) << "Solving the max flow is not optimal!";
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}
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FlowQuantity total_flow_cost = min_cost_flow.GetOptimalCost();
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LOG(INFO) << "Minimum cost flow: " << total_flow_cost;
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LOG(INFO) << "";
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LOG(INFO) << "Arc : Flow / Capacity / Cost";
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for (int i = 0; i < arcs.size(); ++i) {
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LOG(INFO) << graph.Tail(i) << " -> " << graph.Head(i) << ": "
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<< min_cost_flow.Flow(i) << " / " << min_cost_flow.Capacity(i)
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<< " / " << min_cost_flow.UnitCost(i);
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}
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}
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} // namespace operations_research
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int main(int argc, char **argv) {
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google::InitGoogleLogging(argv[0]);
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absl::GetFlag(FLAGS_logtostderr) = 1;
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operations_research::SolveMinCostFlow();
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return EXIT_SUCCESS;
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}
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