Submission #651046

#	Time	Username	Problem	Language	Result	Execution time	Memory
651046		dsyz	Cryptography (NOI20_crypto)	C++17	100 / 100	136 ms	15160 KiB

Crypto

#include <bits/stdc++.h>
using namespace std;
using ll=long long;
#define MAXN (300006)

int n;
ll P[MAXN], f[MAXN], A[MAXN];
vector<ll> d;
struct fen {
	ll fw[MAXN];
	fen() {
		memset(fw, 0, sizeof fw);
	}
	void update(int x,ll nval) {
		for(;x<MAXN;x+=x&(-x)) fw[x]+=nval;
	}
	ll sum(int x) {
		ll res = 0;
		for(;x;x-=x&(-x)) res+=fw[x];
		return res;
	}
} ft;
ll mod=1e9+7;
int main(){
	f[0]=1; for(int i=1;i<MAXN;++i) f[i]=f[i-1]*i%mod; 
	ios::sync_with_stdio(false);
	cin.tie(0);
	cin>>n;
	for(int i=0;i<n;++i) cin>>P[i], d.push_back(P[i]);
	sort(d.begin(), d.end()), d.resize(unique(d.begin(), d.end())-d.begin());
	for(int i=0;i<n;++i) P[i] = lower_bound(d.begin(), d.end(), P[i]) - d.begin() + 1;
	for(int i=n-1;i>=0;--i) {
		A[i] = ft.sum(P[i] - 1);
		ft.update(P[i], 1);
	}
	ll ans = 0;
	for(int i=0;i<n;++i) {
		ans += A[i] * f[n-i-1] % mod;
		ans %= mod;
	}
	cout<<(ans+1)%mod<<'\n';
}

• Subtask 1: 5 / 5
• Subtask 2: 9 / 9
• Subtask 3: 10 / 10
• Subtask 4: 11 / 11
• Subtask 5: 21 / 21
• Subtask 6: 13 / 13
• Subtask 7: 19 / 19
• Subtask 8: 12 / 12