[LG5367] [template] Cantor Expand

Title effect: Given n-$ a $ arranged, find that the whole arrangement ranking in $ $ n-

Solution: Cantor expanded to a full array, there is the first $ I $ $ n + 1-i $ choices, represented by the hexadecimal number change, which is a $ n + 1-i $ hexadecimal. First note arrangement $ [1, i) $ $ I $ than the first number of bits smaller digits $ a $, the first count variable binary bits is $ $ I $ ia-1 $. It can be used Fenwick tree maintenance

Card point: None

 

C++ Code：

#include <cstdio>
#include <iostream>
#include <algorithm>
#define maxn 1000010
#define mul(a, b) (static_cast<long long> (a) * (b) % mod)
const int mod = 998244353;

inline void reduce(int &x) { x += x >> 31 & mod; }
int fac[maxn], ans = 1, n;

namespace BIT {
	int V[maxn], res;
	inline void add(int p) { for (; p <= n; p += p & -p) ++V[p]; }
	inline int query(int p) { for (res = 0; p; p &= p - 1) res += V[p]; return res; }
}

int main() {
	std::ios::sync_with_stdio(false), std::cin.tie(0), std::cout.tie(0);
	std::cin >> n;
	fac[0] = 1;
	for (int i = 1; i <= n; ++i) fac[i] = mul(fac[i - 1], i);
	for (int i = 1, x; i <= n; ++i) {
		std::cin >> x;
		reduce(ans += mul(x - BIT::query(x) - 1, fac[n - i]) - mod);
		BIT::add(x);
	}
	std::cout << ans << '\n';
	return 0;
}