//Union-Find solution
public int FindCircleNum(int[][] M)
{
int n = M.Length;
var uf = new UnionFind(n);
for (int i = 0; i < M.Length; i++)
{
for (int j = 0; j < M[0].Length; j++)
{
if (M[i][j] == 1 && i != j) // i != j (can't be friend to oneself)
{
uf.Union(i, j);
}
}
}
return(uf.ConnectedComponents());
}
private void RemoveBackground(Color[,] image, CIELAB[,] imageLAB)
{
//check perimeter to see if it's mostly black or white
//RGB to LAB
CIELAB black = new CIELAB(0, 0, 0);
CIELAB white = new CIELAB(100, 0, 0);
int width = image.GetLength(0);
int height = image.GetLength(1);
CIELAB[,] labs = imageLAB;//Util.Map<Color, CIELAB>(image, (c) => Util.RGBtoLAB(c));
int numBlack = 0;
int numWhite = 0;
int thresh = 3 * 3;
List<Point> perimeterIdx = new List<Point>();
double totalPerimeter = 4 * width + 4 * height;
double bgThresh = totalPerimeter*0.75;
for (int i = 0; i < width; i++)
{
//top
for (int j = 0; j < 2; j++)
{
if (black.SqDist(labs[i, j])<thresh)
numBlack++;
if (white.SqDist(labs[i, j]) < thresh)
numWhite++;
perimeterIdx.Add(new Point(i, j));
}
//bottom
for (int j = height - 2; j < height; j++)
{
perimeterIdx.Add(new Point(i, j));
if (black.SqDist(labs[i, j]) < thresh)
numBlack++;
if (white.SqDist(labs[i, j]) < thresh)
numWhite++;
}
}
for (int j = 0; j < height; j++)
{
//left
for (int i=0; i<2; i++)
{
perimeterIdx.Add(new Point(i,j));
if (black.SqDist(labs[i, j]) < thresh)
numBlack++;
if (white.SqDist(labs[i, j]) < thresh)
numWhite++;
}
//right
for (int i=width-2; i<width; i++)
{
perimeterIdx.Add(new Point(i, j));
if (black.SqDist(labs[i, j]) < thresh)
numBlack++;
if (white.SqDist(labs[i, j]) < thresh)
numWhite++;
}
}
if (numBlack >= bgThresh || numWhite >= bgThresh)
{
//connected components
UnionFind<CIELAB> uf = new UnionFind<CIELAB>((a,b) => a.SqDist(b)<thresh);
int[,] cc = uf.ConnectedComponents(labs);
SortedSet<int> ids = new SortedSet<int>();
//go around the perimeter to collect the right ids
foreach (Point p in perimeterIdx)
{
if (numWhite > numBlack)
{
if (labs[p.X, p.Y].SqDist(white) < thresh)
ids.Add(cc[p.X, p.Y]);
}
else
{
if (labs[p.X, p.Y].SqDist(black) < thresh)
ids.Add(cc[p.X, p.Y]);
}
}
//fill the bitmap with transparency
for (int i = 0; i < width; i++)
{
for (int j = 0; j < height; j++)
{
if (ids.Contains(cc[i, j]))
image[i, j] = Color.FromArgb(0, 0, 0, 0);
}
}
}
}
private bool ProcessImage(Color[,] image, CIELAB[,] imageLAB)
{
double thresh = 5;
UnionFind<CIELAB> uf = new UnionFind<CIELAB>((a,b)=>(a.SqDist(b)<=thresh));
int[,] assignments = uf.ConnectedComponents(imageLAB);//Util.Map<Color, CIELAB>(image, Util.RGBtoLAB));
int numC = -1;
for(int i=0; i<image.GetLength(0); i++)
for (int j=0; j<image.GetLength(1); j++)
numC = Math.Max(numC, assignments[i,j]+1);
if (numC >= 2)
RemoveBackground(image, imageLAB);
//if it is a black and white image (with num connected components >= 2), it's not a valid color image
return !(isBlackWhite(image, imageLAB) && numC >= 2);
}
