http://codeforces.com/problemset/problem/148/D
#include<cstdio>
#include<string.h>
using namespace std;
#define maxn 1005
double dp[maxn][maxn];
int main()
{
int w,b;
scanf("%d%d",&w,&b);
for(int i=0;i<=b;i++)
dp[0][i]=0.0;
for(int j=1;j<=w;j++)
dp[j][0]=1.0;
for(int i=1;i<=w;i++)
{
for(int j=1;j<=b;j++)
{
dp[i][j]=(double)(i)/(j+i);
if(j>=3) dp[i][j]+=1.0*j/(i+j)*1.0*(j-1)/(i+j-1)*(j-2)/(i+j-2)*dp[i][j-3];
if(j>=2) dp[i][j]+=1.0*j/(i+j)*1.0*(j-1)/(i+j-1)*(i)/(i+j-2)*dp[i-1][j-2];
}
}
printf("%.9f",dp[w][b]);
}
遞歸超時(shí)版本
#include<cstdio>
#include<string.h>
using namespace std;
double probability(double m,double n)
{
if(m<=0) return 0;
if(n<=0) return 1.0;
double val=n/(m+n)*(n-1)/(m+n-1);
return m/(m+n)+val*m/(m+n-2)*probability(m-1,n-2)+val*(n-2)/(m+n-2)*probability(m,n-3);
}
int main()
{
int m,n;
double dm,dn;
scanf("%d%d",&m,&n);
dm=m+0.0,dn=n+0.0;
printf("%.9f",probability(dm,dn));
//printf("%d\n",INF);
}
