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

using System;
using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class MeshIslands
{
    public int[] vertexIsland;
    public int vertexCount;

    public LinkedIndexListArray islandVertices;
    public int islandCount;

    public MeshIslands(MeshAdjacency meshAdjacency)
    {
        LoadFrom(meshAdjacency);
    }

    public void LoadFrom(MeshAdjacency meshAdjacency)
    {
        vertexCount = meshAdjacency.vertexCount;

        ArrayUtils.ResizeCheckedIfLessThan(ref vertexIsland, vertexCount);

        islandCount = 0;
        islandVertices.Allocate(vertexCount, vertexCount);

        for (int i = 0; i != vertexCount; i++)
        {
            vertexIsland[i] = i;
            islandVertices.Append(i, i);
        }

        for (int i = 0; i != vertexCount; i++)
        {
            foreach (int j in meshAdjacency.vertexVertices[i])
            {
                int islandA = vertexIsland[i];
                int islandB = vertexIsland[j];
                if (islandB != islandA)
                {
                    // update vertex->island lookup
                    foreach (int vertex in islandVertices[islandB])
                    {
                        vertexIsland[vertex] = islandA;
                    }

                    // move adjacent island
                    islandVertices.AppendMove(islandA, islandB);
                }
            }
        }

        // remove empty islands
        for (int i = 0; i != vertexCount; i++)
        {
            if (islandVertices.lists[i].size != 0)
                islandVertices.lists[islandCount++] = islandVertices.lists[i];
        }

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

        // update vertex->island lookup
        for (int i = 0; i != islandCount; i++)
        {
            foreach (int vertex in islandVertices[i])
            {
                vertexIsland[vertex] = i;
            }
        }
    }
}