逆序依次為(2,2n-1),(2,2n-2),(2,2n-3).(2,1) -----------n個(gè)
(4,2n-1),(4,2n-2),(4,2n-3).(4,1) -----------n個(gè)
.
(2n,2n-1),(2n,2n-2),(2n,2n-3).(2n,1),------------n個(gè)
(2n-1,2n-2),(2n-1,2n-3).(2n-1,1)-------------n-1個(gè)
(2n-2,2n-3).(2n-2,1)-------------n-2個(gè)
.
(3,1) 1個(gè)
逆序數(shù)為1+2+3+.+n-1+n*n==n(n-1)/2+n^2=(3n^2-n)/2個(gè)?????????????????2n-1?????????1??2n-1??????????????1??3??5,???????????