Submission #164965

#	Time	Username	Problem	Language	Result	Execution time	Memory
164965		coloredrabbit	Ω (kriii4_P3)	C++17	0 / 100	2 ms	376 KiB

P3

#include <cstdio>
const int MOD = 1e9+7;
using ll = long long;
ll _pow(ll a, int n) {
	if (n <= 1) return n % 2 ? a : 1;
	ll h = _pow(a, n >> 1);
	return ((h * h) % MOD) * (n % 2 ? a : 1) % MOD;
}
ll gcd(ll p, ll q) { return !q ? p : gcd(q, p % q); }
ll rev(ll x) { return _pow(x, MOD - 2); }
int main() {
	int P, Q, N, K;
	ll v, ans = 0, A, B, g;
	scanf("%d%d%d%d", &P, &Q, &N, &K);
	if (K == 0 || Q == P) puts("0");
	else if (K == N || Q == 0) puts("1");
	else {
		if(2*Q == P)
			ans = K * rev(N) % MOD;
		else {
			v = Q * rev(P - Q);
			//ans = ((1 - _pow(v, K) + MOD) % MOD) * (rev(1 - _pow(v, N) + MOD) % MOD) % MOD;
			A = (_pow(P - Q, N) - _pow(P - Q, N - K) * _pow(Q, K) % MOD + MOD) % MOD;
			B = (_pow(P - Q, N) - _pow(Q, N) + MOD) % MOD;
			g = gcd(A, B);
			A /= g, B /= g;
			ans = A * rev(B) % MOD;
		}
		printf("%lld", ans);
	}
	
	return 0;
}

Compilation message (stderr)

P3.cpp: In function 'int main()':
P3.cpp:13:5: warning: variable 'v' set but not used [-Wunused-but-set-variable]
  ll v, ans = 0, A, B, g;
     ^
P3.cpp:14:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d%d%d%d", &P, &Q, &N, &K);
  ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 0 / 100