前两天收到的这封邮件，说是要找移动开发者，position provided by "a startup company founded by Max Levchin(www.linkedin.com/in/maxlevchin) who is co-founder of Paypal, LinkedIn, Yelp, Slide."
邮件里附带一个题目，还说 "You must solve this puzzle to apply"：
There're 7 red tiles, 8 blue titles and one white title in a 4 x 4 plane. We could only move the white tile. When moving it, the white tile swaps the position with the adjacent tile. L, R, U, D are corresponding to four directions which the tile could be moved to (Left, Right, Up, Down) For example, starting from configuration (S), by the move sequence RDRDLwe reach the configuration (E). Now, starting from configuration (S), find the shortest way to reach configuration (T).