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OI-codes/S2OJ/1453/1453.cpp

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#include <iostream>
using std::cin;
using std::cout;
const char endl = '\n';
const int N = 1e5 + 5;
const int mod = 998244353;
int t, n, m, fac[N], inv[N], fac_inv[N];
inline int binpow(int a, int b) {
a %= mod;
int res = 1;
while (b) {
if (b & 1) res = static_cast<long long>(res) * a % mod;
a = static_cast<long long>(a) * a % mod;
b >>= 1;
}
return res;
}
inline int C(int n, int m) {
return static_cast<long long>(fac[n]) * fac_inv[m] % mod * fac_inv[n - m] % mod;
}
int main() {
std::ios::sync_with_stdio(false);
cin.tie(nullptr);
fac[0] = 1;
for (int i = 1; i < N; i++) {
fac[i] = static_cast<long long>(fac[i - 1]) * i % mod;
}
inv[0] = inv[1] = 1;
for (int i = 2; i < N; i++) {
inv[i] = static_cast<long long>(mod - mod / i) * inv[mod % i] % mod;
}
fac_inv[0] = fac_inv[1] = 1;
for (int i = 2; i < N; i++) {
fac_inv[i] = static_cast<long long>(fac_inv[i - 1]) * inv[i] % mod;
}
cin >> t;
while (t--) {
cin >> n >> m;
cout << static_cast<long long>(binpow(2, n - m)) * C(n, m) % mod << endl;
}
return 0;
}