康托&康托逆展开

const int Maxn = 1e5 + 5;
const LL Mod = 998244353;

struct Cantor {
	int n;
	int c[Maxn], BIT[Maxn], Bit[Maxn];
	LL order, fac[Maxn];
	
	Cantor () { memset (Bit, 0, sizeof Bit); memset (BIT, 0, sizeof BIT); }
	
	int lowbit (int x) { return x & -x; }
	void Update (int Index, int x, int *str) {
		for (int i = Index; i < Maxn; i += lowbit (i))
			str[i] += x;
	}
	int Sum (int x, int *str) {
		int res = 0;
		for (int i = x; i >= 1; i -= lowbit (i))
			res += str[i];
		return res;
	}
	
	void MakeSet () {
		fac[1] = 1;
		for (int i = 1; i <= n; i++) {
			fac[i] = fac[i - 1] * i;
			fac[i] %= Mod;
		}
	}
	
	LL Get_order () {
		LL sum = 0;
		for (int i = n; i >= 1; i--) {
			sum += (LL)Sum (c[i], BIT) * fac[n - i];
			sum %= Mod;
			Update (c[i], 1, BIT);
		}
		order = sum;
		return sum;
	}
	
	void Get_Seq () {
		LL tem = order - 1;
		for (int i = 1; i <= n; i++) Update (i, 1, Bit);
		for (int i = 1; i <= n; i++) {
			int l = 1, r = n, x = tem / fac[n - i] + 1;
			tem %= fac[n - i];
			while (l + 1 < r) {
				int mid = l + r >> 1;
				if (Sum (mid, Bit) < x)
					l = mid;
				else
					r = mid;
			}
			if (Sum (l, Bit) == x) c[i] = l;
			else c[i] = r;
			Update (c[i], -1, Bit);
		}
	}
};