https://www.youtube.com/watch?v=UJQ-wbb7_gY
https://www.youtube.com/watch?v=aI1pmj-lstE
http://qiita.com/Azunyan1111/items/975c67129d99de33dc21 http://qiita.com/simanezumi1989/items/10cfe1e8a23cd9d4c7b1 http://www.obitko.com/tutorials/genetic-algorithms/japanese/selection.php