Submission #1268189

#	Time	Username	Problem	Language	Result	Execution time	Memory
1268189		aryan	Cryptography (NOI20_crypto)	C++20	100 / 100	135 ms	6284 KiB

Crypto

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

using i64 = long long;
const int mod = 1e9 + 7;

using i64 = long long;

template <class T>
struct fenwick{
    int N;
    vector<T> tree;
    fenwick(int _n){
        N = _n;
        tree = vector<T>(N + 1);
    }
    void update(int i,T v){
        for(++ i;i <= N;i += (i & -i)){
            tree[i] += v;
        }
    }
    T query(int i){
        T val = 0;
        for(++ i;i > 0;i -= (i & -i)){
            val += tree[i];
        }
        return val;
    }
};

int main(){


    int n;
    cin >> n;

    vector<int> fact(n + 1,1);
    vector<int> idx(n);
    for(int i = 1;i <= n;i++){
        fact[i] = (fact[i - 1] * 1LL * i) % mod;
    }


    vector<int> a(n);
    for(int i = 0;i < n;i++){
        cin >> a[i];
    }

    iota(idx.begin(),idx.end(),0);
    sort(idx.begin(),idx.end(),[&](int i,int j){
        return a[i] < a[j];
    });

    for(int i = 0;i < n;i++){
        a[idx[i]] = i + 1;
    }

    fenwick<int> fen(n + 1);

    vector<int> le(n);
    for(int i = 0;i < n;i++){
        fen.update(a[i],1);
        le[i] = fen.query(a[i] - 1);
    }
    int ans = 0;
    for(int i = 0;i < n - 1;i++){
        int totb = a[i] - 1 - le[i];
        assert(totb >= 0);
        ans += (fact[n - i - 1] * 1LL * totb) % mod;
        ans %= mod;
    }
    ans ++;
    ans %= mod;
    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