Submission #1168635

#	Time	Username	Problem	Language	Result	Execution time	Memory
1168635		vibeduck	Cryptography (NOI20_crypto)	C++20	100 / 100	346 ms	30928 KiB

Crypto

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

#define pb push_back
#define pf push_front
#define mp make_pair
#define fi first
#define se second
#define int long long
#define all(x) (x).begin(), (x).end()

typedef long double ld;
typedef long long ll;
typedef pair<ll,ll> pll;
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<bool> vb;
typedef vector<vector<int>> vvi;
typedef vector<vector<bool>> vvb;
typedef vector<vector<ll>> vvll;
typedef vector<string> vs;
typedef vector<vector<string>> vvs;
typedef vector<char> vc;
typedef vector<vector<char>> vvc;
typedef map<int, int> mii;
typedef unordered_map<int, int> umii;

const int mod = 1e9 + 7;
const int inf = INTMAX_MAX;
const bool tc = false;

const int mxn = 3e5 + 5;
int fac[mxn];

void pcomp() {
    fac[0] = 0; fac[1] = 1;
    for (int i = 2; i < mxn; i++) {
        fac[i] = fac[i - 1] * i;
        fac[i] %= mod;
    }
}

struct FenwickTree {
    vector<int> bit;  // binary indexed tree
    int n;

    FenwickTree(int n) {
        this->n = n;
        bit.assign(n, 0);
    }

    FenwickTree(vector<int> const &a) : FenwickTree(a.size()) {
        for (size_t i = 0; i < a.size(); i++)
            add(i, a[i]);
    }

    int sum(int r) {
        int ret = 0;
        for (; r >= 0; r = (r & (r + 1)) - 1)
            ret += bit[r];
        return ret;
    }

    int sum(int l, int r) {
        if (l > r) return 0;
        return sum(r) - sum(l - 1);
    }

    void add(int idx, int delta) {
        for (; idx < n; idx = idx | (idx + 1))
            bit[idx] += delta;
    }
};

inline void solve() {
    int n; cin >> n;
    vi a(n); for (int i = 0; i < n; i++) cin >> a[i];
    vi b = a;
    mii id; sort(all(b)); for (int i = 0; i < n; i++) id[b[i]] = i + 1;
    vi p(n); for (int i = 0; i < n; i++) p[i] = id[a[i]];
    int ans = 1; FenwickTree s(n); for (int i = 0; i < n; i++) s.add(i, 1);

    for (int i = 0; i < n - 1; i++) {
        int sm = s.sum(0, p[i]-2);
        int r = n - 1 - i;
        ans += (sm * fac[r])%mod;
        ans %= mod;
        s.add(p[i]-1, -1);
    }
    cout << ans << '\n';
}

void setIO(string s) {
    freopen((s + ".in").c_str(), "r", stdin);
    freopen((s + ".out").c_str(), "w", stdout);
}

signed main() {
    ios::sync_with_stdio(false);
    cout.tie(0);
    cin.tie(0);
    pcomp();
    //setIO();

    int t = 1;
    if (tc) {
        cin >> t;
    }

    while (t--) {
        solve();
    }
}

Compilation message (stderr)

Crypto.cpp: In function 'void setIO(std::string)':
Crypto.cpp:95:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   95 |     freopen((s + ".in").c_str(), "r", stdin);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Crypto.cpp:96:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   96 |     freopen((s + ".out").c_str(), "w", stdout);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

• 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