function?a?=?binary（ik）
%?return?the?coefficients?of?the?binary?expansion?of?i:i的二的指數(shù)表達(dá)式系數(shù)
%?i?=?a（1）*2^（k-1）?+?a（2）*2^（k-2）?+?...?+?a（k）

if?i>=2^k
???error（‘i?must?be?such?that?i