I - Bag of mice CodeForces -概率DP

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I - Bag of mice
CodeForces - 148D

#include<bits/stdc++.h>
using namespace std;
#define maxn 1111
double dp[2*maxn][maxn];
int w,b;
int main()
{
    scanf("%d%d",&w,&b);
    memset(dp,0.0,sizeof(dp));
    for(int i=1; i<=w; i++)
    {
        dp[i][0]=1.0;
        for(int j=1; j<=b; j++)
        {
            double x=i;
            double y=j;
            //直接获胜
            dp[i][j]+=x/(x+y);
            //两个全抓的黑的之后获胜分两种情况跑出黑的跑出白的
            if(j>=3)
                dp[i][j]+=y/(x+y)*(y-1.0)/(x+y-1.0)*(y-2.0)/(x+y-2.0)*dp[i][j-3];
            if(j>=2)
                dp[i][j]+=y/(x+y)*(y-1.0)/(x+y-1.0)*(x)/(x+y-2.0)*dp[i-1][j-2];
        }
    }
    printf("%.9lf\n",dp[w][b]);
    return 0;
}