ACM notes

cin.tie (NULL);

// TIE stream is two binding function, then return null argument of the current output stream pointer

:: ios :: sync_with_stdio std ( false ); 

// C ++ for compatibility with C, to ensure that the program uses std :: printf and std :: cout when chaos occurs, the output stream tied together. That is "compatible stdio" switch 

// and cin, cout reason for low efficiency, because the first thing you want to enter into the first output buffer, resulting in reduced efficiency, this statement can be used to dispel the iostream input and output buffers,