ICode9

对于长度为2N的括号序列，合法的数量为C(2N,N)/(N+1) 参考：https://blog.csdn.net/ffmpeg4976/article/details/42340379?spm=1001.2101.3001.6650.3&utm_medium=distribute.pc_relevant.none-task-blog-2%7Edefault%7ECTRLIST%7Edefault-3-42340379-blog-105694263.pc_relevant_sort