hdu 5502 Candy Game(dp)

解题思路

代码

#include <cstdio>
#include <cstring>
#include <cmath>
#include <algorithm>

using namespace std;
const int maxn = 1505;

int N;
double P, Q, dp[maxn], f[maxn];

double get (int x) {
double tmp = f[0] = 1, p = pow(P, x);
for (int i = 1; i <= N + 1; i++) {
f[i] = tmp;
//for (int j = max(i-x, 0); j < i; j++)
//f[i] += pow(P, i-j-1) * f[j];
if (i <= N) f[i] *= (1-P);
tmp = tmp * P + f[i];
if (i >= x) tmp -= f[i-x] * p;
}
return f[N+1];
}

double solve () {
dp[0] = 0;
for (int i = 1; i <= N+1; i++)
dp[i] = get(i);
double ans = 0;
for (int i = 1; i <= N+1; i++)
ans += i * (dp[i] - dp[i-1]);
return ans;
}

int main () {
int cas;
scanf("%d", &cas);
while (cas--) {
scanf("%d%lf%lf", &N, &P, &Q);
P = Q / P;
printf("%.3lf\n", solve());
}
return 0;
}