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Convex Hull.py
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Convex Hull.py
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from math import acos, degrees, hypot
def CalcAngle(P1, P2):
if P2[0] < P1[0]:
return 360 - degrees(acos((P2[1] - P1[1]) * 1.0 / hypot(P2[0] - P1[0],
P2[1] - P1[1])))
return round(degrees(acos((P2[1] - P1[1]) * 1.0 / hypot(P2[0] - P1[0],
P2[1] - P1[1]))), 0)
def CalcDistance(P1, P2):
return hypot(P1[0] - P2[0], P1[1] - P2[1])
def checkio(data):
"""list[list[int, int],] -> list[int,]
Find the convex hull.
"""
SortedData = sorted(data, key=lambda x: (x[0], x[1]))
SortedData += [SortedData[0]]
PointList = []
CurrentAngle = 0
CurrentPoint = SortedData[0]
while 1:
PointList.append(CurrentPoint)
SortedData.remove(CurrentPoint)
AngleList = [CalcAngle(CurrentPoint, i) if i != CurrentPoint else 999
for i in SortedData]
MinAngle = min([i for i in AngleList if i >= CurrentAngle])
NextPoint = [j for k, j in enumerate(SortedData)
if AngleList[k] == MinAngle]
# more than one point with same angle
if len(NextPoint) != 1:
DistanceList = [CalcDistance(i, CurrentPoint) for i in NextPoint]
NextPoint = [j for i, j in enumerate(NextPoint)
if DistanceList[i] == min(DistanceList)]
NextPoint = NextPoint[0]
if PointList[0] == NextPoint:
break
else:
CurrentAngle = min([i for i in AngleList
if i >= CurrentAngle])
CurrentPoint = NextPoint
return map(lambda x: data.index(x), PointList)
if __name__ == '__main__':
# These "asserts" using only for self-checking and not necessary for
# auto-testing
assert checkio(
[[7, 6], [8, 4], [7, 2], [3, 2], [1, 6], [1, 8], [4, 9]]
) == [4, 5, 6, 0, 1, 2, 3], "First example"
assert checkio(
[[3, 8], [1, 6], [6, 2], [7, 6], [5, 5], [8, 4], [6, 8]]
) == [1, 0, 6, 3, 5, 2], "Second example"