#include<bits/stdc++.h>
#define ll long long
#define Lowbit(x) (x & (-x))

using namespace std;

const int N = 5e6 + 1000;

struct re{
	ll x, y;
}a[N];

ll n, ansz;
ll t[N];

bool cmp(re a, re b){
	return a.x > b.x;
}

inline void add(ll pos, ll w){
	for (ll i = pos; i <= n; i += Lowbit(i)){
		t[i] += w; 
	}
}

inline ll find(ll pos){
	ll ans = 0;
	for (ll i = pos; i; i -= Lowbit(i)){
		ans += t[i];
	}
	return ans;
}

int main(){
	ios::sync_with_stdio(0);
	cin.tie(0); cout.tie(0);

	cin >> n;
	for (ll i = 1; i <= n; i ++){
		cin >> a[i].x; a[i].y = i;
	} sort(a + 1, a + 1 + n, cmp);
	
	for (ll i = 1; i <= n; i ++){
//		cout << a[i].y << " ";
		add(a[i].y, 1);
		ansz += find(a[i].y) - 1;
	}
	cout << ansz;
	return 0;
}

逆序对中有重复的数字

怎么搞