Submission #493548

#	Time	Username	Problem	Language	Result	Execution time	Memory
493548		dooompy	Cryptography (NOI20_crypto)	C++17	100 / 100	113 ms	9160 KiB

Crypto

#include "bits/stdc++.h"

using namespace std;

using ll = long long;

const ll MOD = 1000000007;

int v[300005], p[300005];
ll fact[300005] = {1};
int bit[300005];

void add(int p) {
    for (; p < 300005; p += (p&(-p))) {
        bit[p]++;
    }
}

int sum(int p) {
    int s = 0;
    for (; p; p -= (p&(-p))) {
        s += bit[p];
    }
    return s;
}

int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0); cout.tie(0);
//    freopen("", "r", stdin);
//    freopen("", "w", stdout);
    int n; cin >> n;
    for (int i = 1; i <= n; i++) {
        cin >> v[i];
        p[i] = v[i];
        fact[i] = (i*fact[i-1]) % MOD;
    }
    sort(p+1, p+n+1);
    ll ans = 0;
    for (int i = 1; i <= n; i++) {
        int pos = lower_bound(p+1, p+n+1, v[i]) - p;
        ans += (fact[n-i] * (pos-1-sum(pos)));
        ans %= (ll)(1e9 + 7);
        add(pos);
    }

    cout << (ans + 1) % (ll) ( 1e9 + 7);
}

• 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