graph: Add assignment_linear_assignment.py sample

ortools/graph/samples/assignment_linear_assignment.py

@@ -0,0 +1,65 @@
+#!/usr/bin/env python3
+# 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]
+"""Solve assignment problem using linear assignment solver."""
+# [START import]
+from ortools.graph import pywrapgraph
+# [END import]
+
+
+def main():
+    """Linear Sum Assignment example."""
+    # [START solver]
+    assignment = pywrapgraph.LinearSumAssignment()
+    # [END solver]
+
+    # [START data]
+    costs = [
+        [90, 76, 75, 70],
+        [35, 85, 55, 65],
+        [125, 95, 90, 105],
+        [45, 110, 95, 115],
+    ]
+    num_workers = len(costs)
+    num_tasks = len(costs[0])
+    # [END data]
+
+    # [START constraints]
+    for worker in range(num_workers):
+        for task in range(num_tasks):
+            if costs[worker][task]:
+                assignment.AddArcWithCost(worker, task, costs[worker][task])
+    # [END constraints]
+
+    # [START solve]
+    status = assignment.Solve()
+    # [END solve]
+
+    # [START print_solution]
+    if status == assignment.OPTIMAL:
+        print(f'Total cost = {assignment.OptimalCost()}\n')
+        for i in range(0, assignment.NumNodes()):
+            print(f'Worker {i} assigned to task {assignment.RightMate(i)}.' +
+                  f'  Cost = {assignment.AssignmentCost(i)}')
+    elif status == assignment.INFEASIBLE:
+        print('No assignment is possible.')
+    elif status == assignment.POSSIBLE_OVERFLOW:
+        print(
+            'Some input costs are too large and may cause an integer overflow.')
+    # [END print_solution]
+
+
+if __name__ == '__main__':
+    main()
+# [END Program]