challenge

refactoredSolution.js

function findRoutes(routes) {
  const { sourcesMap, destinationsMap } = createRoutesMaps(routes);
  const startingPoint = findStartingPoint(sourcesMap, routes);
  const agentRoute = simulateRouteFrom(startingPoint, destinationsMap);

  return agentRoute.join(', ');
}

function simulateRouteFrom(startingPoint, destinationsMap) {
  const routes = [startingPoint];
  let destination = startingPoint;

  while (destination) {
    destination = destinationsMap.get(destination);

    if (destination) {
      routes.push(destination);
    }
  }

  return routes;
}

function findStartingPoint(sourcesMap, routes) {
  for (const [source] of routes) {
    if (!sourcesMap.has(source)) {
      return source;
    }
  }
}

function createRoutesMaps(routes) {
  const sourcesMap = new Map();
  const destinationsMap = new Map();

  routes.forEach(route => {
    const [source, destination] = route;

    sourcesMap.set(destination, source);
    destinationsMap.set(source, destination);
  });

  return { sourcesMap, destinationsMap };
}