【概率DP】51Nod 1398 等公交

题面在这里

考虑fi表示用了i时间，用了任意辆车概率之和

然后就好了

示例程序：

#include<cstdio>#include<cstring>#define cl(x,y) memset(x,y,sizeof(x))inline char nc(){    static char buf[100000],*p1=buf,*p2=buf;    return p1==p2&&(p2=(p1=buf)+fread(buf,1,100000,stdin),p1==p2)?EOF:*p1++;}inline int red(){    int res=0,f=1;char ch=nc();    while (ch<'0'||'9'<ch) {if (ch=='-') f=-f;ch=nc();}    while ('0'<=ch&&ch<='9') res=res*10+ch-48,ch=nc();    return res*f;}const int maxs=200005,maxn=105;int tst,n,s,t[maxn];double p[maxn],f[maxs];int main(){    tst=red();    while (tst--){        n=red(),s=red();        for (int i=1;i<=n;i++)         t[i]=red(),p[i]=red()/100.0;        cl(f,0);        f[0]=1;double ans=0;        for (int i=0;i<s;i++)         for (int j=1;j<=n;j++)          f[i+t[j]]+=f[i]*p[j];        for (int i=s+1;i<=200000;i++)         ans+=(i-s)*f[i];        printf("%.4lf\n",ans);    }    return 0;}