robot.js

const roads = [
  "Alice's House-Bob's House", "Alice's House-Cabin",
  "Alice's House-Post Office", "Bob's House-Town Hall",
  "Daria's House-Ernie's House", "Daria's House-Town Hall",
  "Ernie's House-Grete's House", "Grete's House-Farm",
  "Grete's House-Shop", "Marketplace-Farm",
  "Marketplace-Post Office", "Marketplace-Shop",
  "Marketplace-Town Hall", "Shop-Town Hall"
];

function buildGraph(edges) {
  let graph = Object.create(null);
  function addEdge(from, to) {
    if (graph[from] == null) {
      graph[from] = [to];
    } else {
      graph[from].push(to);
    }
  }
  for (let [from, to] of edges.map(r => r.split("-"))) {
    addEdge(from, to);
    addEdge(to, from);
  }
  return graph;
}

const roadGraph = buildGraph(roads);

class VillageState {
  constructor(place, parcels) {
    this.place = place;
    this.parcels = parcels;
  }
  move(destination) {
    if (!roadGraph[this.place].includes(destination)) {
      return this;
    } else {
      let parcels = this.parcels
        .map(p => {
          if (p.place != this.place) return p;
          return { place: destination, address: p.address };
        })
        .filter(p => p.place != p.address);
      return new VillageState(destination, parcels);
    }
  }
}

let first = new VillageState(
  "Post Office",
  [{ place: "Post Office", address: "Alice's House" }]
);
let next = first.move("Alice's House");

console.log(next.place);
// → Alice's House
console.log(next.parcels);
// → []
console.log(first.place);
// → Post Office

function runRobot(state, robot, memory) {
  for (let turn = 0; ; turn++) {
    if (state.parcels.length == 0) {
      console.log(`Done in ${turn} turns`);
      break;
    }
    let action = robot(state, memory);
    state = state.move(action.direction);
    memory = action.memory;
    console.log(`Moved to ${action.direction}`);
  }

  function randomPick(array) {
    let choice = Math.floor(Math.random() * array.length);
    return array[choice];
  }

  function randomRobot(state) {
    return { direction: randomPick(roadGraph[state.place]) };
  }

  VillageState.random = function (parcelCount = 5) {
    let parcels = [];
    for (let i = 0; i < parcelCount; i++) {
      let address = randomPick(Object.keys(roadGraph));
      let place;
      do {
        place = randomPick(Object.keys(roadGraph));
      } while (place == address);
      parcels.push({ place, address });
    }
    return new VillageState("Post Office", parcels);
  };

  runRobot(VillageState.random(), randomRobot);
  // → Moved to Marketplace
  // → Moved to Town Hall
  // → …
  // → Done in 63 turns

  //Now we will make a more sophsticated not so random but still not so intelligent robot
  
  const mailRoute = [
    "Alice's House", "Cabin", "Alice's House", "Bob's House",
    "Town Hall", "Daria's House", "Ernie's House",
    "Grete's House", "Shop", "Grete's House", "Farm",
    "Marketplace", "Post Office"
  ];

  function routeRobot(state, memory) {
    if (memory.length == 0) {
      memory = mailRoute;
    }
    return { direction: memory[0], memory: memory.slice(1) };
  }

  function findRoute(graph, from, to) {
    let work = [{ at: from, route: [] }];
    for (let i = 0; i < work.length; i++) {
      let { at, route } = work[i];
      for (let place of graph[at]) {
        if (place == to) return route.concat(place);
        if (!work.some(w => w.at == place)) {
          work.push({ at: place, route: route.concat(place) });
        }
      }
    }
  };

  function goalOrientedRobot({ place, parcels }, route) {
    if (route.length == 0) {
      let parcel = parcels[0];
      if (parcel.place != place) {
        route = findRoute(roadGraph, place, parcel.place);
      } else {
        route = findRoute(roadGraph, place, parcel.address);
      }
    }
    return { direction: route[0], memory: route.slice(1) };
  }

  runRobotAnimation(VillageState.random(),
    goalOrientedRobot, []);