B.BonusCards简单dp一下，记\(f_{ij}\)为前i次有j次分给第一类的概率。最后再算上我在第一类被选上的概率即可。constintN=3005;#defineintlonglongintn,a,b;doublef[N][N],g[N][N];signedmain(void){#ifdefONLINE_JUDGE freopen("bonus.in","r",stdin