graph: Add AssignmentMinFlow.java

ortools/graph/samples/AssignmentMinFlow.java

@@ -0,0 +1,104 @@
+// 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]
+package com.google.ortools.graph.samples;
+// [START import]
+import com.google.ortools.Loader;
+import com.google.ortools.graph.MinCostFlow;
+import java.util.ArrayList;
+import java.util.List;
+// [END import]
+
+/** Minimal Assignment Min Flow.*/
+public class AssignmentMinFlow {
+  public static void main(String[] args) throws Exception {
+    Loader.loadNativeLibraries();
+    // [START solver]
+    // Instantiate a SimpleMinCostFlow solver.
+    MinCostFlow minCostFlow = new MinCostFlow();
+    // [END solver]
+
+    // [START data]
+    // Define four parallel arrays: sources, destinations, capacities, and unit costs
+    // between each pair.
+    int[] startNodes = new int[] {
+    0, 0, 0, 0,
+    1, 1, 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 4, 4, 4, 4,
+    5, 6, 7, 8};
+    int[] endNodes = new int[] {
+    1, 2, 3, 4,
+    5, 6, 7, 8, 5, 6, 7, 8, 5, 6, 7, 8, 5, 6, 7, 8,
+    9, 9, 9, 9};
+    int[] capacities = new int[] {
+    1, 1, 1, 1,
+    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+    1, 1, 1, 1};
+    int[] unitCosts = new int[] {
+    0, 0, 0, 0,
+    90, 76, 75, 70, 35, 85, 55, 65, 125, 95, 90, 105, 45, 110, 95, 115,
+    0, 0, 0, 0};
+
+    int source = 0;
+    int sink = 9;
+    // Define an array of supplies at each node.
+    int[] supplies = new int[] {4, 0, 0, 0, 0, 0, 0, 0, 0, -4};
+    // [END data]
+
+    // [START constraints]
+    // Add each arc.
+    for (int i = 0; i < startNodes.length; ++i) {
+      int arc = minCostFlow.addArcWithCapacityAndUnitCost(
+          startNodes[i], endNodes[i], capacities[i], unitCosts[i]);
+      if (arc != i)
+        throw new Exception("Internal error");
+    }
+
+    // Add node supplies.
+    for (int i = 0; i < supplies.length; ++i) {
+      minCostFlow.setNodeSupply(i, supplies[i]);
+    }
+    // [END constraints]
+
+    // [START solve]
+    // Find the min cost flow.
+    MinCostFlow.Status status = minCostFlow.solve();
+    // [END solve]
+
+    // [START print_solution]
+    if (status == MinCostFlow.Status.OPTIMAL) {
+      System.out.println("Total cost: " + minCostFlow.getOptimalCost());
+      System.out.println("");
+      for (int i = 0; i < minCostFlow.getNumArcs(); ++i) {
+        // Can ignore arcs leading out of source or into sink.
+        if (minCostFlow.getTail(i) != source && minCostFlow.getHead(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 (minCostFlow.getFlow(i) > 0) {
+            System.out.println(
+                "Worker " + minCostFlow.getTail(i) +
+                " assigned to task " + minCostFlow.getHead(i) +
+                " Cost: " + minCostFlow.getUnitCost(i));
+          }
+        }
+      }
+    } else {
+      System.out.println("Solving the min cost flow problem failed.");
+      System.out.println("Solver status: " + status);
+    }
+    // [END print_solution]
+  }
+
+  private AssignmentMinFlow() {}
+}
+// [END program]