luogu 1850 换教室 概率+dp

非常好的dp，继续加油练习dp啊

#include<bits/stdc++.h>
#define rep(i,x,y) for(register int i=x;i<=y;i++)

using namespace std;

const int N=2e3+50;
const double inf=1e8+5;
const int V=305;
int n,m,v,e,c[N],d[N],g[V][V];
double k[N],f[N][N][2],ans;

inline int read(){
    int x=0,f=1;char ch=getchar();
    while(!isdigit(ch)){if(ch=='-')f=-1;ch=getchar();}
    while(isdigit(ch)){x=(x<<1)+(x<<3)+(ch^48);ch=getchar();}
    return x*f;}

int main(){
    n=read(),m=read(),v=read(),e=read();
    rep(i,1,n) c[i]=read();
    rep(i,1,n) d[i]=read();
    rep(i,1,n) cin>>k[i];
    memset(g,63,sizeof g); 
    rep(i,1,e){
        int u=read(),v=read(),w=read();
        g[u][v]=g[v][u]=min(g[u][v],w);}
    rep(k,1,v)rep(i,1,v)rep(j,1,v)
        g[i][j]=min(g[i][k]+g[k][j],g[i][j]);
    rep(i,1,v) g[i][i]=g[i][0]=g[0][i]=0;
    rep(i,0,n)rep(j,0,m) f[i][j][0]=f[i][j][1]=inf;
    f[1][0][0]=f[1][1][1]=0;
    rep(i,2,n){
        f[i][0][0]=f[i-1][0][0]+g[c[i-1]][c[i]];
        rep(j,1,min(i,m)){
            int k1=c[i-1],k2=d[i-1],k3=c[i],k4=d[i];
            f[i][j][0]=min(f[i][j][0],f[i-1][j][0]+g[k1][k3]);
            f[i][j][0]=min(f[i][j][0],f[i-1][j][1]+g[k1][k3]*(1-k[i-1])+g[k2][k3]*k[i-1]);
            f[i][j][1]=min(f[i][j][1],f[i-1][j-1][0]+g[k1][k3]*(1-k[i])+g[k1][k4]*k[i]);
            f[i][j][1]=min(f[i][j][1],f[i-1][j-1][1]+g[k1][k3]*(1-k[i-1])*(1-k[i])+g[k2][k3]*k[i-1]*(1-k[i])+g[k1][k4]*(1-k[i-1])*k[i]+g[k2][k4]*k[i-1]*k[i]);
        }
    }ans=inf;
    rep(i,0,m)ans=min(ans,min(f[n][i][0],f[n][i][1]));
    printf("%.2lf\n",ans);return 0;
}

怀挺，下一个