BZOJ 1758: [Wc2010]重建计划 [暂时放弃]

今天晚上思维比较乱，以后再写写吧
#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
typedef long long ll;
const int N=1e5+5,INF=1e9+5;
double eps=1e-4;
inline int read(){
    char c=getchar();int x=0,f=1;
    while(c<'0'||c>'9'){if(c=='-')f=-1;c=getchar();}
    while(c>='0'&&c<='9'){x=x*10+c-'0';c=getchar();}
    return x*f;
}
int n,L,U,a,b;
double w,maxVal,ans;
struct edge{
    int v,ne;
    double w;
}e[N<<1];
int h[N],cnt;
inline void ins(int u,int v,double w){
    cnt++;
    e[cnt].v=v;e[cnt].w=w;e[cnt].ne=h[u];h[u]=cnt;
    cnt++;
    e[cnt].v=u;e[cnt].w=w;e[cnt].ne=h[v];h[v]=cnt;
}

int f[N],size[N],all,vis[N],root;
void dfsRt(int u,int fa){
    size[u]=1;f[u]=0;
    for(int i=h[u];i;i=e[i].ne){
        int v=e[i].v;
        if(vis[v]||v==fa) continue;
        dfsRt(v,u);
        size[u]+=size[v];
        f[u]=max(f[u],size[v]);
    }
    f[u]=max(f[u],all-size[u]);
    if(f[u]<f[root]) root=u;
}

int q[N],head,tail,deep[N];
double val[N],mx[N];
bool visit[N];
void bfs(double g){
    while(head<=tail){
        int u=q[head++];
        for(int i=h[u];i;i=e[i].ne){
            int v=e[i].v;
            if(vis[v]) continue;
            if(!visit[v]){
                visit[v]=1;
                q[++tail]=v;
                deep[v]=deep[u]+1;
                val[v]=val[u]+e[i].w-g;
            }
        }
    }
}
double c[N];
int m;
bool dp(int n){//printf("dp %d %d\n",n,n+m);
    if(m+n<L) return false;
    head=1;tail=0;
    int l=max(L-n,1),r=U-n;
    for(int i=l;i<=r&&i<=m;i++){//printf("ins %d\n",i);
        while(head<=tail&&c[q[tail]]<c[i]) tail--;
        q[++tail]=i;
    }
    for(int i=n;i>=1;i--){//printf("i %d %lf\n",i,mx[i]);
        int l=L-i,r=U-i;//printf("lala %d %d\n",l,r);
        while(head<=tail&&q[head]<l) head++;
        while(head<=tail&&c[r]>c[q[tail]]) tail--;
        q[++tail]=r;
        //printf("qqq %d %d  %lf\n",head,tail,c[q[head]]);
        if(head<=tail&&c[q[head]]+mx[i]>=0) return true;
    }
    return false;
}

bool check(int u,double g){//printf("\ncheck %d %lf\n",u,g);
    for(int i=1;i<=m;i++) c[i]=-INF;m=0;
    for(int i=h[u];i;i=e[i].ne){
        int v=e[i].v;
        if(vis[v]) continue;

                //printf("\nv %d\n",v);
        head=1;tail=0;
        q[++tail]=v;
        deep[v]=1;val[v]=e[i].w-g;
        bfs(g);
        //for(int i=1;i<tail;i++) //printf("%lf ",val[i]);puts("");

        for(int i=1;i<=deep[q[tail]];i++) mx[i]=-INF;
        int id;
        for(int i=1;i<=tail;i++) 
            id=q[i],mx[deep[id]]=max(mx[deep[id]],val[id]),visit[id]=0;
        //for(int i=1;i<=maxDeep;i++) printf("mx %d %lf \n",i,mx[i]);

        if(dp(deep[q[tail]])) return true;
        m=max(m,deep[q[tail]]);
        for(int i=1;i<=deep[q[tail]];i++) c[i]=max(c[i],mx[i]);
    }
    return false;
}

void dfsSol(int u){//printf("dfsSol %d\n",u);if(u!=1) return;
    vis[u]=1;
    double l=ans,r=maxVal;//printf("lr %lf %lf\n\n",l,r);
    while(r-l>eps){
        double mid=(l+r)/2;
        if(check(u,mid)) l=mid;
        else r=mid;
    }
    ans=max(ans,l);
    
    for(int i=h[u];i;i=e[i].ne)
        if(!vis[e[i].v]){
            root=0;all=size[e[i].v];
            if(size[e[i].v]<L) continue;
            dfsRt(e[i].v,0);
            dfsSol(root);
        }
}
int main(){
    freopen("in","r",stdin);
    //freopen("out","w",stdout);
    n=read();L=read();U=read();
    for(int i=1;i<n;i++) 
        a=read(),b=read(),w=read(),ins(a,b,w),maxVal=max(maxVal,w);
    root=0;f[0]=INF;all=n;
    dfsRt(1,0);
    dfsSol(root);
    printf("%.3lf",ans);
}