说明：  十五滑块问题，理工专用，相当靠谱。十五滑块难题是个非常流行的游戏：即使你不知道他的名字，你也一定见过类似的游戏（比如，中国的华容道^_*）。此游戏由15个滑块组成，每个滑块上都标有从1到15不同的数字。所有滑块都放在一个4X4的盒子中，且在这盒子中正好缺少一个滑块。
(Fifteen slider problem, Polytechnic dedicated, very tricky. Fifteen slider puzzle is a very popular game: Even if you do not know his name, you must have seen similar games (for example, China Huarong ^ _*). This game is composed of 15 sliders are labeled from 1 to 15 different numbers on each slide. All sliders are placed in a 4X4 box and just missing a slider in this box.)