Although I quoted Meggido's 32-yr-old LP algorithm in the comments,
a simpler-to-implement randomized algorithm has expected linear time and space complexity.
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![EnclosingCirc][1]
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(Image from [code,project.com](http://www.codeproject.com/Articles/22568/Computational-Geometry-C-and-Wykobi).)
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A clear description of this algorithm may be found at this
lecture prepared by Marc van Kreveld and Maarten Loffler: [PDF slides download](http://www.cs.uu.nl/docs/vakken/ga/slides4b.pdf).


  [1]: https://i.sstatic.net/qnFHO.png