bzoj 5290 [Hnoi2018]道路

http://www.elijahqi.win/archives/3656
https://www.luogu.org/problemnew/show/P4438

终于能独立A题了

一开始思考半天以为神题 其实 考验语文能力

注意1、选n-1条道路 每个城市只且必须选一条

2、乡村之间没有道路

3、最多40条道路到首都

4、每个城市恰好 两条道路 任选其一即可

#include<cstdio>
#include<cctype>
#include<cstring>
#include<algorithm>
#define ll long long
using namespace std;
inline char gc(){
    static char now[1<<16],*S,*T;
    if (T==S){T=(S=now)+fread(now,1,1<<16,stdin);if (T==S) return EOF;}
    return *S++;
}
inline int read(){
    int x=0,f=1;char ch=gc();
    while (!isdigit(ch)) {if (ch=='-') f=-1;ch=gc();}
    while (isdigit(ch)) x=x*10+ch-'0',ch=gc();
    return x*f;
}
const int N=20020;
ll dp[N][41][41];int n,nn,son1[N],son2[N],a[N],b[N],c[N];
inline ll dfs(int x,int a1,int b1){
    if (x>nn) return (ll)c[x-nn]*(a[x-nn]+a1)*(b[x-nn]+b1);
    if (dp[x][a1][b1]!=1LL<<60) return dp[x][a1][b1];
    return dp[x][a1][b1]=min(dfs(son1[x],a1+1,b1)+dfs(son2[x],a1,b1),dfs(son1[x],a1,b1)+dfs(son2[x],a1,b1+1));
}
int main(){
    freopen("bzoj5209.in","r",stdin);
    n=read();nn=n-1;
    for (int i=1;i<n;++i){
        int x=read(),y=read();
        if (x>0) son1[i]=x;else son1[i]=-x+nn;
        if (y>0) son2[i]=y;else son2[i]=-y+nn;
    }
    for (int i=1;i<=n;++i) a[i]=read(),b[i]=read(),c[i]=read();
    for (int i=1;i<=n;++i) for (int j=0;j<=40;++j) for (int k=0;k<=40;++k) dp[i][j][k]=1LL<<60;
    printf("%lld\n",dfs(1,0,0));
    return 0;
}