HanXu questions

• Speed of two algorithms rotating a sequence. (from the book Programming Pearls)
• Django rest framework uploading multiple files
• Why can't I compile this command-line OpenCV Mac application?
• Sound is not played in push notifications
• Spark saving RDD[(Int, Array[Double])] to text file got strange result
• Neo4j create if not exist otherwise update
• Select some from many binary sequences so that the result of "or" them together is 1111111111....111
• pg_trgm behaves differently on Ubuntu and Mac OS X
• Why can Apple declare optional protocol funcs without @objc, and unowned optional variables, but I can't?
• How to do GPU programming on Macbook Air?

HanXu answers