Submission #294551

#	Time	Username	Problem	Language	Result	Execution time	Memory
294551		nandonathaniel	Cryptography (NOI20_crypto)	C++14	100 / 100	161 ms	15976 KiB

Crypto

#include<bits/stdc++.h>
using namespace std;
typedef long long LL;
typedef pair<LL,LL> pii;
const LL MAXN=300005,MOD=1000000007;

LL a[MAXN],bit[MAXN],n,fac[MAXN];

void update(LL now){
	for(LL i=now;i<=n;i+=(i&(-i)))bit[i]++;
}

LL query(LL now){
	LL ret=0;
	if(now==0)return ret;
	for(LL i=now;i>0;i-=(i&(-i)))ret+=bit[i];
	return ret;
}

int main(){
	ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
	fac[0]=1;
	for(LL i=1;i<=MAXN-5;i++)fac[i]=(fac[i-1]*i)%MOD;
	cin >> n;
	vector<pii> v;
	for(LL i=1;i<=n;i++){
		cin >> a[i];
		v.push_back({a[i],i});
	}
	sort(v.begin(),v.end());
	for(int i=0;i<v.size();i++)a[v[i].second]=i+1;
	LL ans=0;
	for(int i=1;i<=n;i++){
		ans=(ans+(((a[i]-1-query(a[i]-1))*fac[n-i])%MOD))%MOD;
		update(a[i]);
	}
	cout << (ans+1)%MOD << '\n';
	return 0;
}

Compilation message (stderr)

Crypto.cpp: In function 'int main()':
Crypto.cpp:31:15: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::pair<long long int, long long int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   31 |  for(int i=0;i<v.size();i++)a[v[i].second]=i+1;
      |              ~^~~~~~~~~

• 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