graph: Add assignment_min_flow.cc

ortools/graph/samples/assignment_min_flow.cc

@@ -0,0 +1,103 @@
+// Copyright 2010-2021 Google LLC
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+// [START program]
+// [START import]
+#include <cstdint>
+
+#include "ortools/graph/min_cost_flow.h"
+// [END import]
+
+namespace operations_research {
+// MinCostFlow simple interface example.
+void AssignmentMinFlow() {
+  // [START solver]
+  // Instantiate a SimpleMinCostFlow solver.
+  SimpleMinCostFlow min_cost_flow;
+  // [END solver]
+
+  // [START data]
+  // Define four parallel arrays: sources, destinations, capacities,
+  // and unit costs between each pair. For instance, the arc from node 0
+  // to node 1 has a capacity of 15.
+  std::vector<int64_t> start_nodes = {
+    0, 0, 0, 0,
+    1, 1, 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 4, 4, 4, 4,
+    5, 6, 7, 8};
+  std::vector<int64_t> end_nodes = {
+    1, 2, 3, 4,
+    5, 6, 7, 8, 5, 6, 7, 8, 5, 6, 7, 8, 5, 6, 7, 8,
+    9, 9, 9, 9};
+  std::vector<int64_t> capacities = {
+    1, 1, 1, 1,
+    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+    1, 1, 1, 1};
+  std::vector<int64_t> unit_costs = {
+    0, 0, 0, 0,
+    90, 76, 75, 70, 35, 85, 55, 65, 125, 95, 90, 105, 45, 110, 95, 115,
+    0, 0, 0, 0};
+
+  int64_t source = 0;
+  int64_t sink = 9;
+  // Define an array of supplies at each node.
+  std::vector<int64_t> supplies = {4, 0, 0, 0, 0, 0, 0, 0, 0, -4};
+  // [END data]
+
+  // [START constraints]
+  // Add each arc.
+  for (int i = 0; i < start_nodes.size(); ++i) {
+    int arc = min_cost_flow.AddArcWithCapacityAndUnitCost(
+        start_nodes[i], end_nodes[i], capacities[i], unit_costs[i]);
+    if (arc != i) LOG(FATAL) << "Internal error";
+  }
+
+  // Add node supplies.
+  for (int i = 0; i < supplies.size(); ++i) {
+    min_cost_flow.SetNodeSupply(i, supplies[i]);
+  }
+  // [END constraints]
+
+  // [START solve]
+  // Find the min cost flow.
+  int status = min_cost_flow.Solve();
+  // [END solve]
+
+  // [START print_solution]
+  if (status == MinCostFlow::OPTIMAL) {
+    LOG(INFO) << "Total cost: " << min_cost_flow.OptimalCost();
+    LOG(INFO) << "";
+    for (std::size_t i = 0; i < min_cost_flow.NumArcs(); ++i) {
+      // Can ignore arcs leading out of source or into sink.
+      if (min_cost_flow.Tail(i) != source && min_cost_flow.Head(i) != sink) {
+        // Arcs in the solution have a flow value of 1. Their start and end nodes
+        // give an assignment of worker to task.
+        if (min_cost_flow.Flow(i) > 0) {
+          LOG(INFO) << "Worker " << min_cost_flow.Tail(i)
+                    << " assigned to task " << min_cost_flow.Head(i)
+                    << " Cost: " << min_cost_flow.UnitCost(i);
+        }
+      }
+    }
+  } else {
+    LOG(INFO) << "Solving the min cost flow problem failed.";
+    LOG(INFO) << "Solver status: " << status;
+  }
+  // [END print_solution]
+}
+
+}  // namespace operations_research
+
+int main() {
+  operations_research::AssignmentMinFlow();
+  return EXIT_SUCCESS;
+}
+// [END program]