1.广度优先搜索 ：仍然有错误，样例8木有通过，明天再fix!Good Night,Baby!
move castle-2.cpp to castle.cpp
castle is ok
数论:Stern-Brocot树

[Reference]Grapham, Kunth and Patashnik. Concrete Mathematics(2th edition). Chapter 4 Number Theory: 4.5 Relative Primality
Fix frac1 output bug
usaco: sort3
usaco holstein
usaco: hamming distance