题面

Sol

第\(i\)道题选对的概率就是\(\frac{min(a[i-1], a[i])}{a[i]*a[i-1]}\)

# include <bits/stdc++.h>

# define RG register

# define IL inline

# define Fill(a, b) memset(a, b, sizeof(a))

using namespace std;

typedef long long ll;

const int _(1e7 + 5);

const int Zsy(1e8 + 1);

IL int Input(){

    RG int x = 0, z = 1; RG char c = getchar();

    for(; c < '0' || c > '9'; c = getchar()) z = c == '-' ? -1 : 1;

    for(; c >= '0' && c <= '9'; c = getchar()) x = (x << 1) + (x << 3) + (c ^ 48);

    return x * z;

}

int n, a[_];

double ans;

int main(RG int argc, RG char* argv[]){

	n = Input(); RG int A = Input(), B = Input(), C = Input(); a[1] = Input();

	for(RG int i = 2; i <= n; ++i) a[i] = (1LL * a[i - 1] * A % Zsy + B) % Zsy;

	for(RG int i = 1; i <= n; ++i) a[i] = a[i] % C + 1;

	a[0] = a[n];

	for(RG int i = 1; i <= n; ++i) ans += 1.0 * min(a[i - 1], a[i]) / (1.0 * a[i] * a[i - 1]);

	printf("%.3lf\n", ans);

	return 0;

}

巴特西

Bzoj2134：单选错位

题面

Sol

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