static double MinCostForAcquiring(IEnumerable<Product> productsToBuy, Purchase startingPoint, IEnumerable<Location> locations, double gasPrice, IDictionary<string, double> memoizer)
{
if (!productsToBuy.Any())
{
return startingPoint.Location.DistanceTo(locations.GetHome()) * gasPrice;
}
string _key = string.Format("{0}:{1}:{2}", startingPoint.Location.Name, startingPoint.IsPerishable.ToString(), productsToBuy.Select(p => p.Name).Aggregate((r, n) => r + ";" + n));
if (memoizer.ContainsKey(_key))
{
return memoizer[_key];
}
var _result = productsToBuy.SelectMany(p => startingPoint.PossiblePurchasesOf(p, locations, gasPrice)
.Select(pur => pur.Cost + MinCostForAcquiring(productsToBuy.Without(p),
pur, locations, gasPrice, memoizer)))
.Min();
memoizer.Add(_key, _result);
return _result;
}
private IEnumerable<Purchase> AllPossiblePurchases(IEnumerable<Location> locations, double gasPrice)
{
if (_purchaseCache == null)
{
_purchaseCache = locations.SelectMany(loc =>
loc.Products.Select(p => new Purchase() {
Location = loc,
Product = p,
IsPerishable = this.IsPerishable & this.Location.IsSameAs(loc) ? true : p.IsPerishable,
Cost = this.IsPerishable & loc.Name != this.Location.Name ? p.Price + this.Location.DistanceToVia(loc, locations.GetHome()) * gasPrice :
p.Price + (this.Location.DistanceTo(loc) * gasPrice)
})
);
}
return _purchaseCache;
}
