Submission #1173786

#	Time	Username	Problem	Language	Result	Execution time	Memory
1173786		ezzzay	Cryptography (NOI20_crypto)	C++20	100 / 100	376 ms	26288 KiB

Crypto

#include<bits/stdc++.h>
using namespace std;
#define ff first
#define ss second
#define pb push_back
#define int long long
const int N=4e5;
int a[N];
int fct[N];
int bit[N];
const int mod=1e9+7;
void update(int idx, int val){
    while(idx<N){
        bit[idx]+=val;
        idx+= idx & -idx;
    }
}
int find(int idx){
    int s=0;
    while(idx>0){
        s+=bit[idx];
        idx-= -idx &idx;
    }
    return s;
}
signed main(){
    int n;
    cin>>n;
    map<int,int>mp;
    for(int i=1;i<=n;i++){
        cin>>a[i];
        mp[a[i]];
    }
    fct[0]=1;
    for(int i=1;i<=n;i++)fct[i]=(fct[i-1]*i)%mod;
    int id=1;
    for(auto it=mp.begin();it!=mp.end();it++){
        it->ss = id++;
    }
    for(int i=1;i<=n;i++){
        a[i]=mp[a[i]];
        update(a[i],1);
    }
    int ans=0;
    fct[0]=0;
    for(int i=1;i<=n;i++){
        int x= find(a[i])-1;
        ans+= (fct[n-i]* (x))%mod;;
        ans%=mod;
        update(a[i],-1);
    }
    cout<<(ans+1)%mod;
}

• 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