101 lines
3.6 KiB
C++
101 lines
3.6 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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// [START program]
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// [START import]
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#include <cstddef>
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#include <cstdint>
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#include <vector>
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#include "ortools/graph/min_cost_flow.h"
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// [END import]
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namespace operations_research {
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// MinCostFlow simple interface example.
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void AssignmentMinFlow() {
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// [START solver]
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// Instantiate a SimpleMinCostFlow solver.
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SimpleMinCostFlow min_cost_flow;
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// [END solver]
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// [START data]
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// Define four parallel arrays: sources, destinations, capacities,
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// and unit costs between each pair. For instance, the arc from node 0
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// to node 1 has a capacity of 15.
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const std::vector<int64_t> start_nodes = {0, 0, 0, 0, 1, 1, 1, 1, 2, 2, 2, 2,
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3, 3, 3, 3, 4, 4, 4, 4, 5, 6, 7, 8};
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const std::vector<int64_t> end_nodes = {1, 2, 3, 4, 5, 6, 7, 8, 5, 6, 7, 8,
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5, 6, 7, 8, 5, 6, 7, 8, 9, 9, 9, 9};
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const std::vector<int64_t> capacities = {1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
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1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1};
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const std::vector<int64_t> unit_costs = {0, 0, 0, 0, 90, 76, 75, 70,
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35, 85, 55, 65, 125, 95, 90, 105,
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45, 110, 95, 115, 0, 0, 0, 0};
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const int64_t source = 0;
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const int64_t sink = 9;
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const int64_t tasks = 4;
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// Define an array of supplies at each node.
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const std::vector<int64_t> supplies = {tasks, 0, 0, 0, 0, 0, 0, 0, 0, -tasks};
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// [END data]
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// [START constraints]
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// Add each arc.
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for (int i = 0; i < start_nodes.size(); ++i) {
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int arc = min_cost_flow.AddArcWithCapacityAndUnitCost(
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start_nodes[i], end_nodes[i], capacities[i], unit_costs[i]);
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if (arc != i) LOG(FATAL) << "Internal error";
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}
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// Add node supplies.
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for (int i = 0; i < supplies.size(); ++i) {
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min_cost_flow.SetNodeSupply(i, supplies[i]);
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}
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// [END constraints]
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// [START solve]
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// Find the min cost flow.
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int status = min_cost_flow.Solve();
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// [END solve]
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// [START print_solution]
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if (status == SimpleMinCostFlow::OPTIMAL) {
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LOG(INFO) << "Total cost: " << min_cost_flow.OptimalCost();
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LOG(INFO) << "";
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for (std::size_t i = 0; i < min_cost_flow.NumArcs(); ++i) {
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// Can ignore arcs leading out of source or into sink.
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if (min_cost_flow.Tail(i) != source && min_cost_flow.Head(i) != sink) {
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// Arcs in the solution have a flow value of 1. Their start and end
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// nodes give an assignment of worker to task.
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if (min_cost_flow.Flow(i) > 0) {
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LOG(INFO) << "Worker " << min_cost_flow.Tail(i)
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<< " assigned to task " << min_cost_flow.Head(i)
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<< " Cost: " << min_cost_flow.UnitCost(i);
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}
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}
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}
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} else {
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LOG(INFO) << "Solving the min cost flow problem failed.";
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LOG(INFO) << "Solver status: " << status;
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}
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// [END print_solution]
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}
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} // namespace operations_research
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int main() {
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operations_research::AssignmentMinFlow();
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return EXIT_SUCCESS;
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}
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// [END program]
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