Submission #504589

#	Time	Username	Problem	Language	Result	Execution time	Memory
504589		Jomnoi	Cryptography (NOI20_crypto)	C++17	100 / 100	621 ms	36220 KiB

Crypto

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

const int N = 3e5 + 10;
const int MOD = 1e9 + 7;

int p[N];
map <int, int> cmp;
int fenwick[N];
long long fac[N];

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

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

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;
    }

    set <int> s;
    for(int i = 1; i <= n; i++) {
        cin >> p[i];
        s.insert(p[i]);
    }

    int cnt = 0;
    for(auto v : s) {
        cmp[v] = ++cnt;
    }

    long long ans = 1;
    for(int i = 1; i <= n; i++) {
        ans = (ans + fac[n - i] * (cmp[p[i]] - query(cmp[p[i]]) - 1) % MOD) % MOD;
        update(cmp[p[i]], 1);
    }
    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