Activation HDU - 4089 （概率DP）

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强

#include <bits/stdc++.h>
using namespace std;
const int MAXN = 2005;
const double eps = 1e-10;
int n, m, k; double p1, p2, p3, p4;
double dp[2][MAXN], c[MAXN], pp[MAXN];
int main() {
	while(~scanf("%d%d%d%lf%lf%lf%lf", &n, &m, &k, &p1, &p2, &p3, &p4)) {
		if(p4 < eps) { puts("0.00000"); continue; }
		double p = p2 / (1 - p1);
		double p31 = p3 / (1 - p1);
		double p41 = p4 / (1 - p1);
		pp[0] = 1;
		for(int i = 1; i <= n; ++i) pp[i] = pp[i-1] * p;
		int now = 0;
		dp[now][1] = p41 / (1 - p);
		c[1] = p41;
		for(int i = 2; i <= n; ++i) {
			now ^= 1;
			for(int j = 2; j <= k; ++j) c[j] = p31 * dp[now^1][j-1] + p41;
			for(int j = k+1; j <= i; ++j) c[j] = p31 * dp[now^1][j-1];
			double tmp = 0;
			for(int j = 1; j <= i; ++j) tmp += pp[i-j] * c[j];
			dp[now][i] = tmp / (1 - pp[i]);
			dp[now][1] = p * dp[now][i] + c[1];
			for(int j = 2; j < i; ++j) dp[now][j] = p * dp[now][j-1] + c[j];
		}
		printf("%.5f\n", dp[now][m]);
	}
}
/*
j==1:    dp[i][1]=p*dp[i][i]+p41;
2<=j<=k: dp[i][j]=p*dp[i][j-1]+p31*dp[i-1][j-1]+p41;
k<j<=i:  dp[i][j]=p*dp[i][j-1]+p31*dp[i-1][j-1];

dp[i][j] = dp[i][j-1] * p + c[j]
*/