com.unity.demoteam.digital-human/Runtime/MeshTools/LinkedIndexListArray.cs

using System;

[Serializable]
public struct LinkedIndexListArray
{
    public LinkedIndexList[] lists;
    public LinkedIndexItem[] items;

    public int listCount;
    public int itemCount;

    public void Allocate(int listCapacity, int itemCapacity)
    {
        ArrayUtils.ResizeCheckedIfLessThan(ref lists, listCapacity);
        ArrayUtils.ResizeCheckedIfLessThan(ref items, itemCapacity);

        Clear();
    }

    public void Clear()
    {
        listCount = lists.Length;
        itemCount = 0;

        for (int i = 0; i != listCount; i++)
        {
            lists[i].head = -1;
            lists[i].size = 0;
        }
    }

    public void Append(int listIndex, int value)
    {
        if (itemCount == items.Length)
        {
            ArrayUtils.ResizeCheckedIfLessThan(ref items, items.Length * 2);
        }

        int headIndex = lists[listIndex].head;
        if (headIndex == -1)
        {
            int itemIndex = itemCount++;

            items[itemIndex] = new LinkedIndexItem
            {
                next = itemIndex,
                prev = itemIndex,
                data = value,
            };

            lists[listIndex].head = itemIndex;
            lists[listIndex].size = 1;
        }
        else
        {
            int itemIndex = itemCount++;
            int tailIndex = items[headIndex].prev;

            items[itemIndex] = new LinkedIndexItem
            {
                next = headIndex,
                prev = tailIndex,
                data = value,
            };

            items[tailIndex].next = itemIndex;
            items[headIndex].prev = itemIndex;

            lists[listIndex].size++;
        }
    }

    public void AppendMove(int listIndex, int listOther)
    {
        int headOther = lists[listOther].head;
        if (headOther != -1)
        {
            int headIndex = lists[listIndex].head;
            if (headIndex != -1)
            {
                int tailIndex = items[headIndex].prev;
                int tailOther = items[headOther].prev;

                items[headIndex].prev = tailOther;
                items[tailIndex].next = headOther;

                items[headOther].prev = tailIndex;
                items[tailOther].next = headIndex;

                lists[listIndex].size += lists[listOther].size;
            }
            else
            {
                lists[listIndex].head = lists[listOther].head;
                lists[listIndex].size = lists[listOther].size;
            }

            lists[listOther].head = -1;
            lists[listOther].size = 0;
        }
    }

    public int GetCount(int listIndex)
    {
        return lists[listIndex].size;
    }

    public LinkedIndexEnumerable this[int listIndex]
    {
        get
        {
            return new LinkedIndexEnumerable(this.items, this.lists[listIndex].head);
        }
    }
}