#969682 (C++17) No.2717 Sum of Subarray of Subsequence

• 問題: No.2717 Sum of Subarray of Subsequence
• ユーザー: Shreyan Ray
• 提出日時: 2024-04-05 21:58:06
• 言語: C++17 (gcc 13.3.0 + boost 1.87.0)
• 結果: AC
• 実行時間: 121 ms / 2,000 ms
• コード長: 2,435 bytes
• コンパイル時間: 2,309 ms
• コンパイル使用メモリ: 199,264 KB
• 最終ジャッジ日時: 2025-02-20 21:20:38
• ジャッジサーバーID （参考情報）: judge5 / judge3

ファイルパターン	結果
sample	AC * 3
other	AC * 21

ソースコード

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#include <bits/stdc++.h>
using namespace std;
#define int long long
#define INF (int)1e18
#define f first
#define s second
mt19937_64 RNG(chrono::steady_clock::now().time_since_epoch().count());
const int facN = 1e6 + 5;
const int mod = 998244353;
int ff[facN], iff[facN];
bool facinit = false;
int power(int x, int y){
    if (y == 0) return 1;
    int v = power(x, y / 2);
    v = 1LL * v * v % mod;
    if (y & 1) return 1LL * v * x % mod;
    else return v;
}
void factorialinit(){
    facinit = true;
    ff[0] = iff[0] = 1;
    for (int i = 1; i < facN; i++){
        ff[i] = 1LL * ff[i - 1] * i % mod;
    }
    iff[facN - 1] = power(ff[facN - 1], mod - 2);
    for (int i = facN - 2; i >= 1; i--){
        iff[i] = 1LL * iff[i + 1] * (i + 1) % mod;
    }
}
int C(int n, int r){
    if (!facinit) factorialinit();
    if (n == r) return 1;
    if (r < 0 || r > n) return 0;
    return 1LL * ff[n] * iff[r] % mod * iff[n - r] % mod;
}
int P(int n, int r){
    if (!facinit) factorialinit();
    assert(0 <= r && r <= n);
    return 1LL * ff[n] * iff[n - r] % mod;
}
int Solutions(int n, int r){
    //solutions to x1 + ... + xn = r 
    //xi >= 0
    return C(n + r - 1, n - 1);
}
void Solve() 
{
    int n; cin >> n;
    vector <int> a(n + 1);
    for (int i = 1; i <= n; i++){
        cin >> a[i];
    }
    int ans = 0;
    auto get = [&](int x){
        int v = x * power(2, x - 1) % mod;
        v += power(2, x);
        v %= mod;
        return v;
    };
    for (int i = 1; i <= n; i++){
        int v = get(n - i);
        // for every element in left side add value 
    //  int ways = v;
    //  ways += (i - 1) * v % mod * (mod + 1) / 2;
    //  ways %= mod;
    
        int ways = v * power(2, i - 1) % mod;
        if (i != 1)
        ways += (i - 1) * v % mod * power(2, i - 2) % mod;
        ways %= mod;
        
    //  cout << ways << "\n";
        ans += ways * a[i];
        ans %= mod;
    }
    cout << ans << "\n";
}
int32_t main() 
{
    auto begin = std::chrono::high_resolution_clock::now();
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    int t = 1;
    // freopen("in",  "r", stdin);
    // freopen("out", "w", stdout);
    
   // cin >> t;
    for(int i = 1; i <= t; i++) 
    {
        //cout << "Case #" << i << ": ";
        Solve();
    }
    auto end = std::chrono::high_resolution_clock::now();
    auto elapsed = std::chrono::duration_cast<std::chrono::nanoseconds>(end - begin);
    cerr << "Time measured: " << elapsed.count() * 1e-9 << " seconds.\n"; 
    return 0;
}
 
 
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