代码:
#include <cassert>//包含cassert函数,cassert函数作用是:如果它的条
//件返回错误,则终止程序执行
#include <cstdio>
#include <vector>
const int N = 1000000;
const int MOD = 998244353;
static inline int inv(int a) {
return a == 1 ? 1 : MOD - 1LL * (MOD / a) * inv(MOD % a) % MOD;
}
#ifndef NO_MAIN
int main() {
//知识点:STL(vector)、简单dp
std::vector<int> factorial(2 * N + 2);
factorial[0] = 1;
for (int i = 1; i <= 2 * N + 1; ++i) {
factorial[i] = 1LL * factorial[i - 1] * i % MOD;
}
int n;
while (scanf("%d", &n) == 1) {
int inv_fact = inv(factorial[2 * n + 1]);
assert(1LL * inv_fact * factorial[2 * n + 1] % MOD == 1);
printf("%d\n", static_cast<int>(1LL * factorial[n] * factorial[n] % MOD *
inv_fact % MOD));
//static_cast是一个c++运算符,功能是把一个表达式转换为某种类型,但没有运行时
//类型检查来保证转换的安全性。
}
}