Book References

1. Thomas H. Cormen, Charles E. Leiserson, Ronald L. Rivest, and Clifford Stein,
   Introduction to Algorithms, 3rd Edition, MIT Press, 2009.
   (Chapter 33: Computational Geometry - Closest Pair of Points)

2. Jon Kleinberg and Eva Tardos,
   Algorithm Design, 1st Edition, Pearson, 2005.
   (Chapter 5: Divide and Conquer - Finding the Closest Pair of Points)

3. Joseph O'Rourke,
   Computational Geometry in C, 2nd Edition, Cambridge University Press, 1998.
   (3.8 Divide and Conquer)

Website References

1. Wikipedia – Closest Pair of Points Problem
   https://en.wikipedia.org/wiki/Closest_pair_of_points_problem