/// <summary>
/// Computes the intersection of this bag with another bag. The intersection of two bags
/// is all items that appear in both of the bags. If an item appears X times in one bag,
/// and Y times in the other bag, the intersection contains the item Minimum(X,Y) times. A new bag is
/// created with the intersection of the bags and is returned. This bag and the other bag
/// are unchanged.
/// </summary>
/// <remarks>
/// <para>When equal items appear in both bags, the intersection will include an arbitrary choice of one of the
/// two equal items.</para>
/// <para>The intersection of two bags is computed in time O(N), where N is the size of the smaller bag.</para>
/// </remarks>
/// <param name="otherBag">Bag to intersection with.</param>
/// <returns>The intersection of the two bags.</returns>
/// <exception cref="InvalidOperationException">This bag and <paramref name="otherBag"/> don't use the same method for comparing items.</exception>
public Bag <T> Intersection(Bag <T> otherBag)
{
CheckConsistentComparison(otherBag);
Bag <T> smaller, larger, result;
if (otherBag.Count > this.Count)
{
smaller = this; larger = otherBag;
}
else
{
smaller = otherBag; larger = this;
}
int copiesInSmaller, copiesInLarger, copies;
// Enumerate each of the items in the smaller bag. Add items that need to be
// added to the intersection.
result = new Bag <T>(keyEqualityComparer);
foreach (T item in smaller.DistinctItems())
{
copiesInLarger = larger.NumberOfCopies(item);
copiesInSmaller = smaller.NumberOfCopies(item);
copies = System.Math.Min(copiesInLarger, copiesInSmaller);
if (copies > 0)
{
result.ChangeNumberOfCopies(item, copies);
}
}
return(result);
}
