Submission #452079

#	Time	Username	Problem	Language	Result	Execution time	Memory
452079		Jomnoi	Cryptography (NOI20_crypto)	C++17	100 / 100	116 ms	9160 KiB

Crypto

#include <bits/stdc++.h>
#define DEBUG 0
#define ll long long
using namespace std;

const int N = 3e5+10;
const int MOD = 1e9+7;
int p[N], a[N];
ll fac[N];
int fenwick[N];

void update(int idx) {
    for(; idx < N; idx += (idx&-idx)) {
        fenwick[idx]++;
    }
}

int query(int idx) {
    int res = 0;
    for(; idx > 0; idx -= (idx&-idx)) {
        res += fenwick[idx];
    }
    return res;
}

bool cmp(int x, int y) {
    return p[x] < p[y];
}

int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    int n;
    cin >> n;
    fac[0] = 1;
    for(int i = 1; i <= n; i++) {
        fac[i] = (fac[i-1]*i)%MOD;
    }
    for(int i = 1; i <= n; i++) {
        cin >> p[i];
        a[i] = i;
    }
    sort(a+1, a+n+1, cmp);
    for(int i = 1; i <= n; i++) {
        p[a[i]] = i;
    }
    ll ans = 1;
    for(int i = 1; i <= n; i++) {
        ans = (ans+fac[n-i]*(p[i]-query(p[i])-1))%MOD;
        update(p[i]);
    }
    cout << ans;
    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