Submission #508665

#	Time	Username	Problem	Language	Result	Execution time	Memory
508665		Joo	Cryptography (NOI20_crypto)	C++17	100 / 100	393 ms	22152 KiB

Crypto

#include <bits/stdc++.h>
using namespace std;

const int N = 3e5+10, mod = 1000000007;

int n, arr[N], fen[N], fac[N];
map<int, int> idx;

void up(int idx, int val){
    if(idx <= 0) return;
    for(; idx < N; idx += idx&-idx) fen[idx] += val;
}

int sum(int idx){
    int res = 0;
    for(; idx; idx -= idx&-idx) res += fen[idx];
    return res;
}

int main(void){
    ios_base::sync_with_stdio(0); cin.tie(0);
    cin >> n;
    vector<int> vec;
    fac[0] = 1;
    for(int i = 1; i <= n ; i++){
        cin >> arr[i];
        vec.emplace_back(arr[i]); 
        up(i, 1);
        fac[i] = 1ll*fac[i-1]*i%mod;
    }

    sort(vec.begin(), vec.end());
    for(int i = 0; i < n; i++) idx[vec[i]] = i+1;

    int ans = 1;
    for(int i = 1; i <= n; i++){
        ans += 1ll*sum(idx[arr[i]]-1)*fac[n-i]%mod;
        ans %= mod;
        up(idx[arr[i]], -1);
    }
    cout << ans << "\n";


    return 0;
}

• 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