Submission #19767

#	Time	Username	Problem	Language	Result	Execution time	Memory
19767		Qwaz	괄호 (kriii4_R)	C++14	100 / 100	137 ms	1084 KiB

R

#include <cstdio>

typedef long long ll;
const int MOD = 1000000007;

ll modpow(ll a, ll x) {
	ll ret = 1;
	a = a % MOD;

	while (x) {
		if (x & 1) ret = ret * a % MOD;
		a = a * a % MOD;
		x >>= 1;
	}

	return ret;
}

int main() {
	int n, k;
	scanf("%d%d", &n, &k);

	ll res = 1, catalan = 1, xk = 1;
	for (int i = 2; i <= n+1; i++) {
		if (i & 1) {
			res = res * (k+1) % MOD;
		} else {
			res = (res * (k+1) - catalan * xk) % MOD;
			if (res < 0) res += MOD;

			int t = (i >> 1) - 1;
			catalan = 2 * (2*t + 1) * modpow(t+2, MOD-2) % MOD * catalan % MOD;
			xk = xk * k % MOD;
		}
	}

	printf("%lld\n", res);

	return 0;
}

• Subtask 1: 8 / 8
• Subtask 2: 92 / 92