/// <summary>Remove the value at the specified location</summary>
/// <param name="level">Index of the level (0-based)</param>
/// <param name="offset">Offset in the level (0-based)</param>
/// <returns>Value that was removed</returns>
public T RemoveAt(int level, int offset)
{
Contract.Assert(level >= 0 && offset >= 0 && offset < 1 << level);
//TODO: check if level is allocated ?
var segment = m_levels[level];
Contract.Assert(segment != null && segment.Length == 1 << level);
T removed = segment[offset];
if (level == 0)
{ // removing the last inserted value
segment[0] = default(T);
}
else if (level == 1)
{ // split the first level in two
if (IsFree(0))
{ // move up to root
// ex: remove 'b' at (1,1) and move the 'a' back to the root
// 0 [_] => [a]
// 1 [a,b] => [_,_]
m_root[0] = segment[1 - offset];
segment[0] = default(T);
segment[1] = default(T);
}
else
{ // merge the root in missing spot
// ex: remove 'b' at (1,1) and move the 'c' down a level
// N = 3 N = 2
// 0 [c] => 0 [_]
// 1 [a,b] => 1 [a,c]
ColaStore.MergeSimple <T>(segment, m_root[0], segment[1 - offset], m_comparer);
m_root[0] = default(T);
}
}
else if ((m_count & 1) == 1)
{ // Remove an item from an odd-numbered set
// Since the new count will be even, we only need to merge the root in place with the level that is missing a spot
// ex: replace the 'b' at (2,1) with the 'e' in the root
// N = 5 N = 4
// 0 [e] => 0 [_]
// 1 [_,_] 1 [_,_]
// 2 [a,b,c,d] => 2 [a,c,d,e]
ColaStore.MergeInPlace <T>(segment, offset, m_root[0], m_comparer);
m_root[0] = default(T);
}
else
{
// we are missing a spot in out modified segment, that need to fill
// > we will take the first non empty segment, and break it in pieces
// > its last item will be used to fill the empty spot
// > the rest of its items will be spread to all the previous empty segments
// find the first non empty segment that can be broken
int firstNonEmptyLevel = ColaStore.LowestBit(m_count);
if (firstNonEmptyLevel == level)
{ // we are the first level, this is easy !
// move the empty spot at the start
if (offset > 0)
{
Array.Copy(segment, 0, segment, 1, offset);
}
// and spread the rest to all the previous levels
ColaStore.SpreadLevel(level, m_levels);
//TODO: modify SpreadLevel(..) to take the offset of the value to skip ?
}
else
{ // break that level, and merge its last item with the level that is missing one spot
// break down this level
T tmp = ColaStore.SpreadLevel(firstNonEmptyLevel, m_levels);
// merge its last item with the empty spot in the modified level
ColaStore.MergeInPlace(m_levels[level], offset, tmp, m_comparer);
}
}
--m_count;
if (m_levels.Length > MAX_SPARE_ORDER)
{ // maybe release the last level if it is empty
ShrinkIfRequired();
}
CheckInvariants();
return(removed);
}
