fenwick treeによる転倒数と使い方

class Fenwick_Tree:
    def __init__(self, n):
        self._n = n
        self.data = [0] * n

    def add(self, p, x):
        assert 0 <= p < self._n
        p += 1
        while p <= self._n:
            self.data[p - 1] += x
            p += p & -p

    def sum(self, l, r):
        assert 0 <= l <= r <= self._n
        return self._sum(r) - self._sum(l)

    def _sum(self, r):
        s = 0
        while r > 0:
            s += self.data[r - 1]
            r -= r & -r
        return s
N = int(input())
A = list(map(int,input().split()))
bit = Fenwick_Tree(N)
ans0 = 0
for n in range(N):
    bit.add(A[n],1)
    ans0 += n+1 - bit._sum(A[n]+1)
print(ans0)
for k in range(N-1):
    ans0 = ans0+N-A[k]*2-1
    print(ans0)
自分より小さいものの数とか数えていける。