/// <summary>
/// Modifies this data structure to also contains all unions from other.
/// </summary>
/// <param name="other"></param>
/// <returns>Whether this object was changed</returns>
public bool CopyUnions(DisjointSets <T> other)
{
// Create a temporary reverse mapping of other's items to its entries - O(n)
var otherItemsToEntries = new Dictionary <DisjointSetItem, T>();
foreach (var kvp in other.entriesToItems)
{
otherItemsToEntries[kvp.Value] = kvp.Key;
}
// Unite each of other's entries with its representative only - O(n)
bool ret = false;
foreach (var entryAndSetItem in other.entriesToItems)
{
var entry = entryAndSetItem.Key;
var item = entryAndSetItem.Value;
if (item.IsSingle() == true)
{
continue;
}
other.Find(item);
var repEntry = otherItemsToEntries[item.parent];
bool wasOnlyUnitedNow = this.Union(entry, repEntry);
ret = ret || wasOnlyUnitedNow;
}
return(ret);
}
public DisjointSets(DisjointSets <T> other)
{
entriesToItems = new Dictionary <T, DisjointSetItem>();
maxRank = other.maxRank;
var queue = new Queue <T>(other.entriesToItems.Keys);
var otherRepsToNewReps = new Dictionary <DisjointSetItem, DisjointSetItem>();
while (queue.Count != 0)
{
var entry = queue.Dequeue();
var item = other.entriesToItems[entry];
other.Find(item); // Makes item.parent point directly do the set's representative
if (item.parent == item) // This is the set's representative
{
var newItem = new DisjointSetItem();
entriesToItems[entry] = newItem;
// .parent already points to itself as needed
newItem.rank = item.rank; // Since all items in a set do not point directly to the set's rep,
// the set's rank would have been 1 regardless of its size, had it
// been created by calls to Union. We prefer to remember the original rank.
otherRepsToNewReps[item] = newItem;
}
else
{
if (otherRepsToNewReps.ContainsKey(item.parent)) // We've copied this rep already
{
var newItem = new DisjointSetItem();
entriesToItems[entry] = newItem;
newItem.parent = otherRepsToNewReps[item.parent];
// .rank not important in non-rep items
}
else
{
queue.Enqueue(entry); // Wait for the rep to be copied first.
}
}
}
}
