Number of Boomerangs in Python

PythonServer Side ProgrammingProgramming

Suppose we have n points in the plane that are all pairwise distinct. Now a "boomerang" is a tuple of points like (i, j, k) such that the distance between i and j is the same as the distance between i and k. We have to find the number of boomerangs.

So, if the input is like [[0,0],[1,0],[2,0]], then the output will be 2, as two boomerangs are [[1,0],[0,0],[2,0]] and [[1,0],[2,0],[0,0]].

To solve this, we will follow these steps −

  • counter_of_boomerangs := 0

  • for each point_1 in points array, do

    • x1, y1 = point_1

    • define a map called distance_count_dict

    • for each point_2 in points array, do

      • x2, y2 = point_2

      • diff_x := x2 - x1

      • diff_y := y2 - y1

      • dist := diff_x^2 + diff_y^2

      • distance_count_dict[ dist ] := distance_count_dict[ dist ] + 1

    • for each d in distance_count_dict −

      • n := distance_count_dict[d]

      • counter_of_boomerangs := counter_of_boomerangs + n * (n - 1)

  • return counter_of_boomerangs

Example 

Let us see the following implementation to get better understanding −

 Live Demo

from collections import defaultdict
class Solution:
   def numberOfBoomerangs(self, points):
      counter_of_boomerangs = 0
      for point_1 in points:
         x1, y1 = point_1
         distance_count_dict = defaultdict( int )
         for point_2 in points:
            x2, y2 = point_2
            diff_x = x2-x1
            diff_y = y2-y1
            dist = diff_x ** 2 + diff_y ** 2
            distance_count_dict[ dist ] += 1
         for d in distance_count_dict:
            n = distance_count_dict[d]
            counter_of_boomerangs += n * (n-1)
      return counter_of_boomerangs

ob = Solution()
print(ob.numberOfBoomerangs([[0,0],[1,0],[2,0]]))

Input

[[0,0],[1,0],[2,0]]

Output

0
raja
Published on 10-Jun-2020 16:18:55
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