bzoj1758 [Wc2010]重建计划

  1 //It is made by wfj_2048~
  2 #include <algorithm>
  3 #include <iostream>
  4 #include <complex>
  5 #include <cstring>
  6 #include <cstdlib>
  7 #include <cstdio>
  8 #include <vector>
  9 #include <cmath>
 10 #include <queue>
 11 #include <stack>
 12 #include <map>
 13 #include <set>
 14 #define inf (1e18)
 15 #define eps (3e-4)
 16 #define N (100010)
 17 #define ls (x<<1)
 18 #define rs (x<<1|1)
 19 #define il inline
 20 #define RG register
 21 #define ll long long
 22 #define min(a,b) (a<b ? a : b)
 23 #define max(a,b) (a>b ? a : b)
 24 #define File(s) freopen(s".in","r",stdin),freopen(s".out","w",stdout)
 25  
 26 using namespace std;
 27  
 28 struct edge{ int nt,to,dis; }g[N<<1];
 29  
 30 int head[N],st[N],vi[N],vi1[N],vis[N],dep[N],son[N],sz[N],ss[N],RT[N][19],Dp[N][19],n,l,r,num,top,bit,Mx_dep;
 31 double sum[N<<2],dis[N],mx[N],L,R,mid,res,ans;
 32  
 33 il int gi(){
 34     RG int x=0,q=1; RG char ch=getchar();
 35     while ((ch<‘0‘ || ch>‘9‘) && ch!=‘-‘) ch=getchar();
 36     if (ch==‘-‘) q=-1,ch=getchar();
 37     while (ch>=‘0‘ && ch<=‘9‘) x=x*10+ch-48,ch=getchar();
 38     return q*x;
 39 }
 40  
 41 il void insert(RG int from,RG int to,RG int dis){
 42     g[++num]=(edge){head[from],to,dis},head[from]=num; return;
 43 }
 44 
 45 il void build(){ for (RG int i=1;i<=bit+n;++i) sum[i]=-inf; return; }
 46 
 47 il void update0(RG int x,RG double y){
 48     for (x+=bit,sum[x]=max(sum[x],y),x>>=1;x;x>>=1) sum[x]=max(sum[ls],sum[rs]); return;
 49 }
 50 
 51 il void update1(RG int x){
 52     for (sum[x+=bit]=-inf,x>>=1;x;x>>=1) sum[x]=-inf; return;
 53 }
 54 
 55 il double query(RG int l,RG int r){
 56     RG double res=-inf;
 57     for (l+=bit-1,r+=bit+1;l^r^1;l>>=1,r>>=1){
 58     if (~l&1) res=max(res,sum[l^1]);
 59     if (r&1) res=max(res,sum[r^1]);
 60     }
 61     return res;
 62 }
 63 
 64 il void getroot(RG int x,RG int p,RG int S,RG int &rt){
 65     sz[x]=1,son[x]=0; RG int v;
 66     for (RG int i=head[x];i;i=g[i].nt){
 67     v=g[i].to; if (v==p || vis[v]) continue;
 68     getroot(v,x,S,rt),sz[x]+=sz[v];
 69     son[x]=max(son[x],sz[v]);
 70     }
 71     son[x]=max(son[x],S-sz[x]);
 72     if (son[rt]>=son[x]) rt=x; return;
 73 }
 74 
 75 il void getdep(RG int x,RG int p){
 76     dep[x]=dep[p]+1,Mx_dep=max(Mx_dep,dep[x]); RG int v;
 77     for (RG int i=head[x];i;i=g[i].nt){
 78     v=g[i].to; if (v==p || vis[v]) continue;
 79     getdep(v,x);
 80     }
 81     return;
 82 }
 83 
 84 il void getdis(RG int x,RG int p,RG double key){
 85     dep[x]=dep[p]+1,sz[x]=1; RG int v,k=dep[x];
 86     if (!vi[k]) st[++top]=k,vi[k]=1; mx[k]=max(mx[k],dis[x]);
 87     for (RG int i=head[x];i;i=g[i].nt){
 88     v=g[i].to; if (v==p || vis[v]) continue;
 89     dis[v]=dis[x]+g[i].dis-key;
 90     getdis(v,x,key),sz[x]+=sz[v];
 91     }
 92     return;
 93 }
 94 
 95 il void solve0(RG int x,RG int S,RG int level){
 96     RG int rt=0,v; Mx_dep=0,son[0]=S;
 97     getroot(x,0,S,rt),vis[rt]=1,RT[x][level]=rt;
 98     for (RG int i=head[rt];i;i=g[i].nt){
 99     v=g[i].to; if (!vis[v]) getdep(v,0);
100     }
101     Dp[x][level]=Mx_dep;
102     for (RG int i=head[rt];i;i=g[i].nt){
103     v=g[i].to; if (!vis[v]) solve0(v,sz[v],level+1);
104     }
105     return;
106 }
107 
108 il int solve(RG int x,RG int S,RG int level,RG double key){
109     RG int rt=RT[x][level],Mx=Dp[x][level],tp=0,v; vis[rt]=1;
110     for (bit=1;bit<=Mx+1;bit<<=1);
111     for (RG int i=head[rt];i;i=g[i].nt){
112     v=g[i].to; if (vis[v]) continue;
113     top=0,dis[v]=g[i].dis-key,getdis(v,0,key);
114     for (RG int j=1,L,R,k;j<=top;++j){
115         k=st[j]; if (l<=k && k<=r) res=max(res,mx[k]); if (res>eps) return 1;
116         if (!vi1[k]) ss[++tp]=k,vi1[k]=1; L=max(l-k,1),R=min(r-k,Mx);
117         if (L<=R) res=max(res,mx[k]+query(L,R)); if (res>eps) return 1;
118     }
119     for (RG int j=1,k;j<=top;++j)
120         k=st[j],update0(k,mx[k]),mx[k]=-inf,vi[k]=0;
121     }
122     for (RG int i=1;i<=tp;++i) update1(ss[i]),vi1[ss[i]]=0;
123     for (RG int i=head[rt];i;i=g[i].nt){
124     v=g[i].to; if (!vis[v]) if (solve(v,sz[v],level+1,key)) return 1;
125     }
126     return res>eps;
127 }
128 
129 il void work(){
130     n=gi(),l=gi(),r=gi(),L=inf;
131     for (RG int i=1,u,v,w;i<n;++i)
132     u=gi(),v=gi(),w=gi(),insert(u,v,w),insert(v,u,w),L=min(L,w),R=max(R,w);
133     solve0(1,n,0);
134     while (R-L>eps){
135     mid=(L+R)*0.5,res=-inf; for (bit=1;bit<=n+1;bit<<=1); build();
136     for (RG int i=1;i<=n;++i) mx[i]=-inf,vi[i]=vi1[i]=vis[i]=0;
137     if (solve(1,n,0,mid)) ans=mid,L=mid; else R=mid;
138     }
139     printf("%0.3lf\n",ans); return;
140 }
141  
142 int main(){
143     File("rebuild");
144     work();
145     return 0;
146 }