// Test for closest pairs to P in set sS (P is a point in the strip)
PointSet testStripPoint(PointSet S, Point P,
PointSet sS, Point M, Boolean lookDIR)
{
Point Q;
// Draw P's bounding box
if (DELAY > 50)
{
drawDQBoundingBox(S, P, M, lookDIR);
pause(DELAY);
}
for (int j = 0; j < sS.points.Count; j++)
{
Q = sS.pointAt(j);
// if Q is in P's bounding box
//if ((Math.Abs(P.x - Q.x) <= S.dmin) &&
//(Math.Abs(P.y - Q.y) <= S.dmin))
//{
// draw a red segment to show that it is being compared
if (DELAY > 50)
{
drawSegment(P, Q);
pause(DELAY);
}
numComparisons++;
S = testBoundingBoxPoint(S, P, Q);
// erase the red segment after the comparison
if (DELAY > 50)
{
eraseSegment(P, Q, Color.Yellow);
pause(DELAY);
}
//}
}
// Erase P's bounding box
if (DELAY > 50) { drawDQStrip(S, M); }
return S;
}
public double ClosestPairDQ(PointSet S, ref PointSet current)
{
if (S.points.Count <= 1)
{
S.dmin = inf;
}
else
{
// calculate co-ordinates of median point
int median = (int)Math.Ceiling((decimal)S.points.Count / 2);
Point M = S.pointAt(median - 1);
// calculate two subproblems (median in first subset)
PointSet S1 = subSet(S, 0, median - 1);
PointSet S2 = subSet(S, median, S.points.Count - 1);
// highlight the whole set
if (DELAY > 50)
{
drawField(S, Color.Cyan);
drawVertical(M, Color.Blue);
pause(DELAY);
eraseVertical(M);
eraseField(S);
}
// recursively calculate solutions to sub-problems
S.dmin = Math.Min(ClosestPairDQ(S1, ref current), ClosestPairDQ(S2, ref current));
// highlight the whole set, and solutions for each subset
if (DELAY > 50)
{
drawField(S, Color.Cyan);
drawVertical(M, Color.Blue);
pause(DELAY);
}
// merge two sub-solutions
S = merge(S, S1, S2, ref current);
// highlight set in gray b/c solution has been computed
if (DELAY > 50)
{
eraseVertical(M);
eraseField(S);
drawField(S, Color.LightGray);
pause(DELAY);
}
}
return S.dmin;
}
// returns a subset of containing the elements of S from fromIndex to
// toIndex inclusive
public PointSet subSet(PointSet S, int fromIndex, int toIndex)
{
PointSet T = new PointSet();
for (int i = fromIndex; i <= toIndex; i++)
{
T.add(S.pointAt(i));
}
return T;
}
PointSet merge(PointSet S, PointSet S1, PointSet S2, ref PointSet WorkSet)
{
Point M = S1.pointAt(S1.points.Count - 1);
// draw the strip about the median
if (DELAY > 50)
{
drawDQStrip(S, M);
pause(DELAY);
}
for (int i = 0; i < S.points.Count; i++)
{
Point P = S.pointAt(i);
if (Math.Abs(P.x - M.x) <= S.dmin)
{
// P is in S1, only look in S2
if (S1.contains(P))
{
S = testStripPoint(S, P, S2, M, true);
}
// P is in S2, only look in S1
if (S2.contains(P))
{
S = testStripPoint(S, P, S1, M, false);
}
// update miniMUM distance
if (S.dmin < WorkSet.dmin)
{
WorkSet.dmin = S.dmin;
if (WorkSet.closestPair.Count == 0)
{
WorkSet.closestPair.Add(S.closestPair[0]);
WorkSet.closestPair.Add(S.closestPair[1]);
}
else
{
WorkSet.closestPair[0] = S.closestPair[0];
WorkSet.closestPair[1] = S.closestPair[1];
}
}
}
}
return S;
}
public void drawPoints(PointSet S, Color c)
{
for (int i = 0; i < S.points.Count; i++)
{
Point P = S.pointAt(i);
drawPoint(P);
}
}
