Submission #693817

#	Time	Username	Problem	Language	Result	Execution time	Memory
693817		saayan007	Cryptography (NOI20_crypto)	C++17	100 / 100	87 ms	15124 KiB

Crypto

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

using ll = long long;
using pi = pair<int, int>;
using pl = pair<ll, ll>;
using vi = vector<int>;
using vl = vector<ll>;
using vpi = vector<pi>;
using vpl = vector<pl>;

#define fur(i, a, b) for(ll i = a; i <= (ll) b; ++i)
#define ruf(i, a, b) for(ll i = a; i >= (ll) b; --i)
#define fr first
#define sc second
#define mp make_pair
#define pb push_back
#define eb emplace_back
#define all(x) (x).begin(),(x).end()
#define rall(x) (x).rbegin(),(x).rend()
#define nl "\n"

const ll mod = 1e9L + 7;
const ll mxn = 3e5L + 5;

ll n;
pl p[mxn];
ll fact[mxn];

ll mul(const ll &a, const ll &b) {
    ll c = (a % mod) * (b % mod);
    c %= mod;
    if(c < 0)
        c += mod;
    return c;
}

ll sum(const ll &a, const ll &b) {
    ll c = (a % mod) + (b % mod);
    c %= mod;
    if(c < 0)
        c += mod;
    return c;
}

ll fen[mxn] = {};

void upd(ll pos, ll val) {
    while(pos <= n) {
        fen[pos] += val;
        pos += pos & -pos;
    }
}

ll qry(ll pos) {
    ll res = 0;
    while(pos >= 1) {
        res += fen[pos];
        pos -= pos & -pos;
    }
    return res;
}

int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);

    cin >> n;
    fur(i, 1, n) {
        cin >> p[i].fr;
        p[i].sc = i;
    }
    sort(p + 1, p + n + 1);
    ll a[n + 1];
    fur(i, 1, n) {
        a[p[i].sc] = i;
    }

    fact[0] = fact[1] = 1;
    fur(i, 2, n) {
        fact[i] = mul(fact[i - 1], i);
    }

    fur(i, 1, n)
        upd(i, 1);
    ll dp[n + 1] = {};
    ll res = 0;
    fur(i, 1, n) {
        ll smaller = qry(a[i] - 1);
        dp[i] = mul(smaller, fact[n - i]);
        res = sum(res, dp[i]);
        upd(a[i], -1);
    }
    res = sum(res, 1);
    cout << res << nl;
}

• 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