Submission #19310

#	Time	Username	Problem	Language	Result	Execution time	Memory
19310		hongjun7	Σ (kriii4_P2)	C++98	100 / 100	16 ms	1240 KiB

P2

#include <stdio.h>
int mod = 1e9 + 7;
long long f(long long a, long long b) {
	if (b == 0) return 1;
	if (b == 1) return a;
	long long v = f(a, b / 2);
	v = (v*v) % mod;
	if (b & 1) v = (v*a) % mod;
	return v;
}
long long mul(long long a, long long b) {
	return (a*b) % mod;
}
long long div(long long a, long long b) {
	return (a * f(b, mod - 2)) % mod;
}
long long a[10005], b[10005];
int main() {
	int m;
	long long N = 1, X = 0;
	scanf("%d", &m);
	for (int i = 1; i <= m; i++) {
		scanf("%lld%lld", &b[i], &a[i]);
		N = mul(N, b[i]);
	}
	for (int i = 1; i <= m; i++) {
		long long g = div(N, b[i]);
		long long v = mul(a[i], g);
		X = (X + v) % mod;
	}
	X = div(X, N);
	printf("%lld", X);
}

• Subtask 1: 100 / 100