【BZOJ1419】 Red is good [期望DP]

 1 #include<iostream>  
 2 #include<string>  
 3 #include<algorithm>  
 4 #include<cstdio>  
 5 #include<cstring>  
 6 #include<cstdlib>  
 7 #include<cmath>
 8 using namespace std; 
 9 typedef long long s64; 
10  
11 const int ONE = 5001;
12 const int E6 = 1e6;
13  
14 int n,m;
15 double f[2][5001];
16  
17 int get() 
18 {
19         int res=1,Q=1;  char c;
20         while( (c=getchar())<48 || c>57)
21         if(c==‘-‘)Q=-1;
22         if(Q) res=c-48; 
23         while((c=getchar())>=48 && c<=57) 
24         res=res*10+c-48; 
25         return res*Q; 
26 }
27  
28  
29 int main()
30 {
31         n=get();    m=get();
32         for(int i=0,A=0; i<=n; i++,A^=1)
33         {
34             f[A][0] = i;
35             for(int j=0; j<=m; j++)
36                 f[A][j] = max(0.0, (double)i/(i+j) * (f[A^1][j]+1) + (double)j/(i+j) * (f[A][j-1]-1) );
37         }
38         s64 record = floor(f[n&1][m] * E6);
39         printf("%lld.%06lld", record/E6, record%E6);
40 }