zoj 3329 One Person Game (概率DP )

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There is a very simple and interesting one-person game. You have 3 dice, namely Die1, Die2 and Die3. Die1 has K₁ faces. Die2 has K₂ faces. Die3 has K₃ faces. All the dice are fair dice, so the probability of rolling each value, 1 to K₁, K₂, K₃ is exactly 1 / K₁, 1 / K₂ and 1 / K₃. You have a counter, and the game is played as follow:

1. Set the counter to 0 at first.
2. Roll the 3 dice simultaneously. If the up-facing number of Die1 is a, the up-facing number of Die2 is b and the up-facing number of Die3 is c, set the counter to 0. Otherwise, add the counter by the total value of the 3 up-facing numbers.
3. If the counter‘s number is still not greater than n, go to step 2. Otherwise the game is ended.

Calculate the expectation of the number of times that you cast dice before the end of the game.

Input

There are multiple test cases. The first line of input is an integer T (0 < T <= 300) indicating the number of test cases. Then T test cases follow. Each test case is a line contains 7 non-negative integers n, K₁, K₂, K₃, a, b, c (0 <= n <= 500, 1 < K₁, K₂, K₃ <= 6, 1 <= a <= K₁, 1 <= b <= K₂, 1 <= c <= K₃).

Output

For each test case, output the answer in a single line. A relative error of 1e-8 will be accepted.

Sample Input

2
0 2 2 2 1 1 1
0 6 6 6 1 1 1

Sample Output

1.142857142857143
1.004651162790698

思路：dp[i]=∑(dp[i+k]*p[k])+dp[0]*p0+1;  (k=3..k1+k2+k3) //dp[i]：从该点走到游戏结束的期望步数。

因为对于固定的k1、k2、k3，求得dp[0]是一个定值。

可以设dp[i]=A[i]*dp[0]+B[i]; 带入上式可以得到dp[i]=(∑(p[k]*A[i+k])+p0)dp[0]+∑(p[k]*A[i+k])+p0;

A[i]=∑(p[k]*A[i+k])+p0;

B[i]=∑(p[k]*A[i+k])+p0;

则：dp[0]=(1-A[i])/B[0];

#include<stdio.h>
#include<math.h>
#include<string.h>
#include<stdlib.h>
#include<algorithm>
#include<iostream>
using namespace std;
#define N 550        <span style="white-space: pre-wrap; font-family: 'Microsoft YaHei';">//数组不能开小了!!</span>
#define LL __int64
const int inf=0x1f1f1f1f;
const double eps=1e-10;
double p[20],A[N],B[N],p0;
int main()
{
    int T,i,j,k,n,a,b,c,k1,k2,k3;
    scanf("%d",&T);
    while(T--)
    {
        scanf("%d%d%d%d%d%d%d",&n,&k1,&k2,&k3,&a,&b,&c);
        double p0=1.0/(k1*k2*k3);
        memset(p,0,sizeof(p));
        for(i=1; i<=k1; i++)
        {
            for(j=1; j<=k2; j++)
            {
                for(k=1; k<=k3; k++)
                {
                    if(i==a&&j==b&&k==c)
                        continue;
                    p[i+j+k]+=p0;
                }
            }
        }
        memset(A,0,sizeof(A));
        memset(B,0,sizeof(B));
        for(i=n; i>=0; i--)
        {
            A[i]=p0;
            B[i]=1;
            for(j=1; j<=(k1+k2+k3); j++)
            {
                A[i]+=A[i+j]*p[j]; 
                B[i]+=B[i+j]*p[j];
            }
        }
        printf("%.10f\n",B[0]/(1.0-A[0]));
    }
    return 0;
}

zoj 3329 One Person Game (概率DP )

标签：style   blog   color   io   os   ar   for   strong   sp   

原文地址：http://blog.csdn.net/u011721440/article/details/40150221