Angular Sweep in Python

# python program to find the maximum number of
# points that can be enclosed by a fixed-radius
# circle
import math

MAX_POINTS = 500
arr = [0] * MAX_POINTS
dis = [[0 for i in range(MAX_POINTS)] for j in range(MAX_POINTS)]

# This function returns the maximum points that
# can lie inside the circle of radius 'r' being
# rotated about point 'i'
def mycompare(A, B):
    if A[0] < B[0]:
        return True
    elif A[0] > B[0]:
        return False
    else:
        return A[1] == 1

def getPointsInside(i, r, n):
      
    #  This vector stores alpha and beta and flag
    # is marked true for alpha and false for beta
    angles = []

    for j in range(n):
        if i != j and dis[i][j] <= 2*r:
          
              # acos returns the arc cosine of the complex
            # used for cosine inverse
            B = math.acos(dis[i][j]/(2*r))
            
            # arg returns the phase angle of the complex
            A = math.atan2(arr[j].imag - arr[i].imag, arr[j].real - arr[i].real)
            alpha = A - B
            beta = A + B
            angles.append([alpha, True])
            angles.append([beta, False])

    # angles vector is sorted and traversed
    angles.sort(key=lambda x: (x[0], x[1] == 1))

    # count maintains the number of points inside
    # the circle at certain value of theta
    # res maintains the maximum of all count
    count = 1
    res = 1
    for angle in angles:
      
          # entry angle
        if angle[1]:
            count += 1
            
        # exit angle
        else:
            count -= 1
        res = max(res, count)

    return res

# Returns count of maximum points that can lie
# in a circle of radius r.
def maxPoints(arr, n, r):
  
      # dis array stores the distance between every
    # pair of points
    for i in range(n - 1):
        for j in range(i + 1, n):
          
              # abs gives the magnitude of the complex
            # number and hence the distance between
            # i and j
            dis[i][j] = dis[j][i] = abs(arr[i] - arr[j])

    # This loop picks a point p
    ans = 0
    for i in range(n):
      
          # maximum number of points for point arr[i]
        ans = max(ans, getPointsInside(i, r, n))

    return ans

# Driver code
r = 1
arr = [complex(6.47634, 7.69628),
       complex(5.16828, 4.79915),
       complex(6.69533, 6.20378)]
n = len(arr)
print("The maximum number of points are:", maxPoints(arr, n, r))