Submission #38485145

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Source Code Expand

#include<bits/stdc++.h>
#define LL long long
#define MOD 998244353
using namespace std;
int mul(const int &a, const int &b)
{
    return 1LL * a * b % MOD;
}
void Inc(int &a, const int &b)
{
    ((a += b) >= MOD) && (a -= MOD);
}
void Mul(int &a, const int &b)
{
    a = 1LL * a * b % MOD;
}
void Sqr(int &a)
{
    a = 1LL * a * a % MOD;
}
int qwqmi(int x, int k = MOD - 2)
{
    int res = 1;
    while(k)
    {
        if(k & 1) Mul(res, x);
        Sqr(x), k >>= 1;
    }
    return res;
}
const int N = 1e7 + 5;
int fac[2 * N], facinv[2 * N], th[N];
void preprocess()
{
    fac[0] = facinv[0] = th[0] = 1;
    for(int i = 1; i < 2 * N; ++i)
        fac[i] = mul(fac[i - 1], i);
    facinv[2 * N - 1] = qwqmi(fac[2 * N - 1]);
    for(int i = 2 * N - 2; i >= 1; --i)
        facinv[i] = mul(facinv[i + 1], i + 1);
    for(int i = 1; i < N; ++i)
        th[i] = mul(th[i - 1], 3);
}
int binom(int n, int m)
{
    if(n < m) return 0;
    return mul(fac[n], mul(facinv[m], facinv[n - m]));
}
int n, ans;
int main()
{
    preprocess();
    scanf("%d", &n);
    for(int i = 0; i <= 2 * n && n - 1 - 2 * i >= 0; ++i)
    {
        int w = 1;
        Mul(w, binom(2 * n, i));
        Mul(w, binom(2 * n - i, n - 1 - 2 * i));
        Mul(w, th[n - 1 - 2 * i]);
        Inc(ans, w);
    }
    Mul(ans, qwqmi(n));
    printf("%d\n", ans);
    return 0;
}

Submission Info

Compile Error

./Main.cpp: In function ‘int main()’:
./Main.cpp:53:10: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
   53 |     scanf("%d", &n);
      |     ~~~~~^~~~~~~~~~

Judge Result