ortools-clone/examples/notebook/contrib/bus_schedule.ipynb

{
 "cells": [
  {
   "cell_type": "markdown",
   "id": "google",
   "metadata": {},
   "source": [
    "##### Copyright 2025 Google LLC."
   ]
  },
  {
   "cell_type": "markdown",
   "id": "apache",
   "metadata": {},
   "source": [
    "Licensed under the Apache License, Version 2.0 (the \"License\");\n",
    "you may not use this file except in compliance with the License.\n",
    "You may obtain a copy of the License at\n",
    "\n",
    "    http://www.apache.org/licenses/LICENSE-2.0\n",
    "\n",
    "Unless required by applicable law or agreed to in writing, software\n",
    "distributed under the License is distributed on an \"AS IS\" BASIS,\n",
    "WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.\n",
    "See the License for the specific language governing permissions and\n",
    "limitations under the License.\n"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "basename",
   "metadata": {},
   "source": [
    "# bus_schedule"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "link",
   "metadata": {},
   "source": [
    "<table align=\"left\">\n",
    "<td>\n",
    "<a href=\"https://colab.research.google.com/github/google/or-tools/blob/main/examples/notebook/contrib/bus_schedule.ipynb\"><img src=\"https://raw.githubusercontent.com/google/or-tools/main/tools/colab_32px.png\"/>Run in Google Colab</a>\n",
    "</td>\n",
    "<td>\n",
    "<a href=\"https://github.com/google/or-tools/blob/main/examples/contrib/bus_schedule.py\"><img src=\"https://raw.githubusercontent.com/google/or-tools/main/tools/github_32px.png\"/>View source on GitHub</a>\n",
    "</td>\n",
    "</table>"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "doc",
   "metadata": {},
   "source": [
    "First, you must install [ortools](https://pypi.org/project/ortools/) package in this colab."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "install",
   "metadata": {},
   "outputs": [],
   "source": [
    "%pip install ortools"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "description",
   "metadata": {},
   "source": [
    "\n",
    "\n",
    "  Bus scheduling in Google CP Solver.\n",
    "\n",
    "\n",
    "  Problem from Taha \"Introduction to Operations Research\", page 58.\n",
    "\n",
    "  This is a slightly more general model than Taha's.\n",
    "\n",
    "  Compare with the following models:\n",
    "  * MiniZinc: http://www.hakank.org/minizinc/bus_scheduling.mzn\n",
    "  * Comet   : http://www.hakank.org/comet/bus_schedule.co\n",
    "  * ECLiPSe : http://www.hakank.org/eclipse/bus_schedule.ecl\n",
    "  * Gecode  : http://www.hakank.org/gecode/bus_schedule.cpp\n",
    "  * Tailor/Essence'  : http://www.hakank.org/tailor/bus_schedule.eprime\n",
    "  * SICStus: http://hakank.org/sicstus/bus_schedule.pl\n",
    "\n",
    "  This model was created by Hakan Kjellerstrand (hakank@gmail.com)\n",
    "  Also see my other Google CP Solver models:\n",
    "  http://www.hakank.org/google_or_tools/\n",
    "\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "code",
   "metadata": {},
   "outputs": [],
   "source": [
    "import sys\n",
    "from ortools.constraint_solver import pywrapcp\n",
    "\n",
    "\n",
    "def main(num_buses_check=0):\n",
    "\n",
    "  # Create the solver.\n",
    "  solver = pywrapcp.Solver(\"Bus scheduling\")\n",
    "\n",
    "  # data\n",
    "  time_slots = 6\n",
    "  demands = [8, 10, 7, 12, 4, 4]\n",
    "  max_num = sum(demands)\n",
    "\n",
    "  # declare variables\n",
    "  x = [solver.IntVar(0, max_num, \"x%i\" % i) for i in range(time_slots)]\n",
    "  num_buses = solver.IntVar(0, max_num, \"num_buses\")\n",
    "\n",
    "  #\n",
    "  # constraints\n",
    "  #\n",
    "  solver.Add(num_buses == solver.Sum(x))\n",
    "\n",
    "  # Meet the demands for this and the next time slot\n",
    "  for i in range(time_slots - 1):\n",
    "    solver.Add(x[i] + x[i + 1] >= demands[i])\n",
    "\n",
    "  # The demand \"around the clock\"\n",
    "  solver.Add(x[time_slots - 1] + x[0] == demands[time_slots - 1])\n",
    "\n",
    "  if num_buses_check > 0:\n",
    "    solver.Add(num_buses == num_buses_check)\n",
    "\n",
    "  #\n",
    "  # solution and search\n",
    "  #\n",
    "  solution = solver.Assignment()\n",
    "  solution.Add(x)\n",
    "  solution.Add(num_buses)\n",
    "\n",
    "  collector = solver.AllSolutionCollector(solution)\n",
    "  cargs = [collector]\n",
    "\n",
    "  # objective\n",
    "  if num_buses_check == 0:\n",
    "    objective = solver.Minimize(num_buses, 1)\n",
    "    cargs.extend([objective])\n",
    "\n",
    "  solver.Solve(\n",
    "      solver.Phase(x, solver.CHOOSE_FIRST_UNBOUND, solver.ASSIGN_MIN_VALUE),\n",
    "      cargs)\n",
    "\n",
    "  num_solutions = collector.SolutionCount()\n",
    "  num_buses_check_value = 0\n",
    "  for s in range(num_solutions):\n",
    "    print(\"x:\", [collector.Value(s, x[i]) for i in range(len(x))], end=\" \")\n",
    "    num_buses_check_value = collector.Value(s, num_buses)\n",
    "    print(\" num_buses:\", num_buses_check_value)\n",
    "\n",
    "  print()\n",
    "  print(\"num_solutions:\", num_solutions)\n",
    "  print(\"failures:\", solver.Failures())\n",
    "  print(\"branches:\", solver.Branches())\n",
    "  print(\"WallTime:\", solver.WallTime())\n",
    "  print()\n",
    "  if num_buses_check == 0:\n",
    "    return num_buses_check_value\n",
    "\n",
    "\n",
    "print(\"Check for minimun number of buses\")\n",
    "num_buses_check = main()\n",
    "print(\"... got \", num_buses_check, \"buses\")\n",
    "print(\"All solutions:\")\n",
    "main(num_buses_check)\n",
    "\n"
   ]
  }
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