ZHANG, Ruda December 30, 2018:  Use dollar style math markup. [1b7036c]
ZHANG, Ruda March 23, 2018:  Global remove trailing whitespaces [2b7ff90]
Ruda Zhang December 06, 2016:  Dijkstra's algorithm. [e96b984]
Ruda Zhang July 05, 2016:  Rename Chinese title to English. [26be649]