81 lines
2.6 KiB
C++
81 lines
2.6 KiB
C++
// Copyright 2010-2025 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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// From Taha 'Introduction to Operations Research', example 6.4-2."""
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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 "absl/base/log_severity.h"
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#include "absl/log/globals.h"
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#include "ortools/base/init_google.h"
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#include "ortools/graph/max_flow.h"
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// [END import]
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namespace operations_research {
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// MaxFlow simple interface example.
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void SimpleMaxFlowProgram() {
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// [START solver]
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// Instantiate a SimpleMaxFlow solver.
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SimpleMaxFlow max_flow;
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// [END solver]
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// [START data]
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// Define three parallel arrays: start_nodes, end_nodes, and the capacities
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// between each pair. For instance, the arc from node 0 to node 1 has a
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// capacity of 20.
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std::vector<int64_t> start_nodes = {0, 0, 0, 1, 1, 2, 2, 3, 3};
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std::vector<int64_t> end_nodes = {1, 2, 3, 2, 4, 3, 4, 2, 4};
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std::vector<int64_t> capacities = {20, 30, 10, 40, 30, 10, 20, 5, 20};
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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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max_flow.AddArcWithCapacity(start_nodes[i], end_nodes[i], capacities[i]);
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}
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// [END constraints]
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// [START solve]
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// Find the maximum flow between node 0 and node 4.
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int status = max_flow.Solve(0, 4);
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// [END solve]
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// [START print_solution]
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if (status == SimpleMaxFlow::OPTIMAL) {
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LOG(INFO) << "Max flow: " << max_flow.OptimalFlow();
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LOG(INFO) << "";
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LOG(INFO) << " Arc Flow / Capacity";
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for (std::size_t i = 0; i < max_flow.NumArcs(); ++i) {
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LOG(INFO) << max_flow.Tail(i) << " -> " << max_flow.Head(i) << " "
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<< max_flow.Flow(i) << " / " << max_flow.Capacity(i);
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}
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} else {
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LOG(INFO) << "Solving the max flow problem failed. Solver status: "
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<< 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(int argc, char* argv[]) {
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InitGoogle(argv[0], &argc, &argv, true);
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absl::SetStderrThreshold(absl::LogSeverityAtLeast::kInfo);
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operations_research::SimpleMaxFlowProgram();
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return EXIT_SUCCESS;
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}
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// [END program]
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