81 lines
2.8 KiB
C++
81 lines
2.8 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/min_cost_flow.h"
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#include <utility>
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#include <vector>
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#include "absl/flags/flag.h"
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#include "ortools/base/init_google.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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// 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 = {
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{{0, 1}, 15, 4}, {{0, 2}, 8, 4}, {{1, 2}, 20, 2},
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{{1, 3}, 4, 2}, {{1, 4}, 10, 6}, {{2, 3}, 15, 1},
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{{2, 4}, 4, 3}, {{3, 4}, 20, 2}, {{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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absl::SetFlag(&FLAGS_stderrthreshold, 0);
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InitGoogle(argv[0], &argc, &argv, true);
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operations_research::SolveMinCostFlow();
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return EXIT_SUCCESS;
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}
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