UVA 10529 - Dumb Bones (概率dp)

 1 #include <bits/stdc++.h>
 2 
 3 using namespace std;
 4 const int maxn = 1100;
 5 int n;
 6 double l,r;
 7 double dp[maxn];
 8 double calc (int n,int x)
 9 {
10     return (1.0+l*dp[x-1]+r*dp[n-x])/(1-l-r)+dp[x-1]+dp[n-x];
11 }
12 int main()
13 {
14     //freopen("de.txt","r",stdin);
15     while (~scanf("%d",&n)){
16         if (n==0) break;
17         scanf("%lf%lf",&l,&r);
18         dp[0]=0;
19         dp[1]=1.0/(1-r-l);
20         for (int i=2;i<=n;++i){
21             dp[i]=calc(i,i);
22             for (int j=1;j<=i;++j)
23                 dp[i]=min(dp[i],calc(i,j));
24         }
25         printf("%.2f\n",dp[n]);
26     }
27     return 0;
28 }

 1 #include<iostream>  
 2 #include<cstdio>  
 3 using namespace std;  
 4 double f[100005];  
 5 double pl,pr,ans;  
 6 int n;  
 7 inline double cal(int n,int i){  
 8     return (pl*f[i-1]+pr*f[n-i]+1)/(1.0-pl-pr)+f[i-1]+f[n-i];//计算期望   
 9 }  
10 int main(){  
11     cin>>n;  
12     int i,j,x=1;  
13     cin>>pl>>pr;  
14     f[0]=0;f[1]=1.0/(1.0-pl-pr);//初始化，0张牌期望为0，一张牌期望为既不左倒也不右倒的概率   
15     for(i=2;i<=n;i++){  
16         f[i]=cal(i,x);  
17         while(x<i&&cal(i,x+1)<f[i]){f[i]=cal(i,x+1);x++;}//更优的决策点一定在上一次决策点之后   
18     }  
19     printf("%.2lf",f[n]);//保留两位   
20     return 0;  
21 }