static ListDualStack <int> ConvexHullGrahamScan2(Point[] points)
{
var hull = new ListDualStack <int>();
var sortedIndeces = Enumerable.Range(0, points.Length)
.OrderBy(x => points[x].Y)
.ToArray();
hull.Add(sortedIndeces[0]);
hull.Add(sortedIndeces[1]);
for (int i = 2; i < sortedIndeces.Length; ++i)
{
while (hull.Count > 1)
{
var area = DirectedArea(
points[hull.SecondLast],
points[hull.Last],
points[sortedIndeces[i]]);
if (area > Epsillon)
{
break;
}
hull.RemoveLast();
}
hull.Add(sortedIndeces[i]);
}
for (int i = sortedIndeces.Length - 2; i >= 0; --i)
{
while (hull.Count > 1)
{
var area = DirectedArea(
points[hull.SecondLast],
points[hull.Last],
points[sortedIndeces[i]]);
if (area > Epsillon)
{
break;
}
hull.RemoveLast();
}
hull.Add(sortedIndeces[i]);
}
hull.RemoveLast();
return(hull);
}
static ListDualStack <int> ConvexHullGrahamScan(Point[] points)
{
var hull = new ListDualStack <int>();
var firstIndex = 0;
for (int i = 1; i < points.Length; ++i)
{
if (points[firstIndex].Y > points[i].Y)
{
firstIndex = i;
}
}
hull.Add(firstIndex);
var firstPoint = points[firstIndex];
var sortedPoints = new int[points.Length - 1];
for (int i = 0; i < sortedPoints.Length; ++i)
{
if (i == firstIndex)
{
sortedPoints[i] = points.Length - 1;
}
else
{
sortedPoints[i] = i;
}
}
Array.Sort(sortedPoints, (ia, ib) =>
{
var a = points[ia];
var b = points[ib];
var area = DirectedArea(firstPoint, a, b);
if (area < -Epsillon)
{
return(1);
}
if (area > Epsillon)
{
return(-1);
}
return(0);
});
hull.Add(sortedPoints[0]);
for (int i = 1; i < sortedPoints.Length; ++i)
{
var currIndex = sortedPoints[i];
while (true)
{
var area = DirectedArea(
points[hull.SecondLast],
points[hull.Last],
points[currIndex]);
if (area > Epsillon)
{
break;
}
hull.RemoveLast();
}
hull.Add(currIndex);
}
while (true)
{
var area = DirectedArea(
points[hull.SecondLast],
points[hull.Last],
points[hull.First]);
if (area > Epsillon)
{
break;
}
hull.RemoveLast();
}
return(hull);
}
