( ) HDU 4159 Indomie

#include<iostream>#include<algorithm>#include<cmath>#include<stdio.h>#include<queue>#include<map>#include<set>#include<vector>#include<string>#include<ctime>#include<string.h>using namespace std; #define pi acos(-1.0)#define INF 0x7fffffffffffffff#define bug puts("hear!")#define inf 0x7fffffff#define eps 1e-8#define FRE freopen("in.txt","r",stdin)#define E exp(1.0)double c[51][51];double a[51]; void init(){ int i,j;    c[1][1]=1,c[1][0]=1;    for(i=2;i<=50;i++)    {        c[i][0]=c[i][i]=1;        for(j=1;j<i;j++)        {            c[i][j]=c[i-1][j]+c[i-1][j-1];        }    }    a[0]=1,a[1]=2;    for(i=2;i<=50;i++)    {        a[i]=a[i-1]*2;    }} int main(){    int n,m;    init();    while(scanf("%d%d",&n,&m)!=-1)    {        if(n<m)        {            puts("100.00000");            continue;        }        double sum=0;        for(int i=0;i<=m;i++)        {            sum+=c[n][i]*a[n-i];        }        double x=sum-c[n][m]*a[n-m];        printf("%.5lf\n",x*100/sum);    }    return 0;}