81 lines
2.5 KiB
Python
81 lines
2.5 KiB
Python
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"""Simple Travelling Salesperson Problem (TSP) between cities."""
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from ortools.constraint_solver import routing_enums_pb2
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from ortools.constraint_solver import pywrapcp
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def create_data_model():
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"""Stores the data for the problem."""
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data = {}
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data["distance_matrix"] = [
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[99, 2, 3, 1, 99, 99],
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[99, 99, 99, 2, 2, 4],
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[3, 99, 99, 2, 2, 99],
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[1, 2, 99, 99, 99, 99],
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[99, 99, 2, 2, 99, 1],
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[99, 4, 3, 99, 1, 99],
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]
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data["num_vehicles"] = 1
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data["depot"] = 0
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return data
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def print_solution(manager, routing, solution):
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"""Prints solution on console."""
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print(f"Objective: {solution.ObjectiveValue()} miles")
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index = routing.Start(0)
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plan_output = "Route for vehicle 0:\n"
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route_distance = 0
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while not routing.IsEnd(index):
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plan_output += f" {manager.IndexToNode(index) + 1} ->"
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previous_index = index
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index = solution.Value(routing.NextVar(index))
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route_distance += routing.GetArcCostForVehicle(previous_index, index, 0)
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plan_output += f" {manager.IndexToNode(index)}\n"
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plan_output += f"Route distance: {route_distance} miles\n"
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print(plan_output)
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def main():
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"""Entry point of the program."""
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# Instantiate the data problem.
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data = create_data_model()
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# Create the routing index manager.
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manager = pywrapcp.RoutingIndexManager(
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len(data["distance_matrix"]), data["num_vehicles"], data["depot"]
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)
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# Create Routing Model.
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routing = pywrapcp.RoutingModel(manager)
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def distance_callback(from_index, to_index):
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"""Returns the distance between the two nodes."""
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# Convert from routing variable Index to distance matrix NodeIndex.
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from_node = manager.IndexToNode(from_index)
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to_node = manager.IndexToNode(to_index)
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return data["distance_matrix"][from_node][to_node]
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transit_callback_index = routing.RegisterTransitCallback(distance_callback)
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# Define cost of each arc.
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routing.SetArcCostEvaluatorOfAllVehicles(transit_callback_index)
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# Setting first solution heuristic.
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search_parameters = pywrapcp.DefaultRoutingSearchParameters()
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search_parameters.first_solution_strategy = (
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routing_enums_pb2.FirstSolutionStrategy.PATH_CHEAPEST_ARC
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)
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# Solve the problem.
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solution = routing.SolveWithParameters(search_parameters)
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# Print solution on console.
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if solution:
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print_solution(manager, routing, solution)
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if __name__ == "__main__":
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main()
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