51Nod 1766 树上的最远点对

#include<cstdio>
#include<cmath>
#include<cstring>
#include<utility>
#include<vector>
#include<iostream>
using namespace std;

#define debug(a) cout<<#a<<"="<<a<<" "
#define mpr make_pair
typedef pair< int,int > pr;
typedef long long LL;
const int N = 100050;
const int M = 25;

int n,m,cnt;
vector< pr > g[N];
int pow2[M],lg2[N<<1],dfs[N<<1],d[N],val[N],pos[N];
int f[N<<1][M];

inline int in(int x=0,char ch=getchar()){ while(ch>‘9‘ || ch<‘0‘) ch=getchar();
	while(ch>=‘0‘ && ch<=‘9‘) x=(x<<3)+(x<<1)+ch-‘0‘,ch=getchar();return x; }
void DFS(int u,int fa,int dep,int value){
	dfs[++m]=u,d[u]=dep,val[u]=value,pos[u]=m,f[m][0]=u;
	for(int i=0,v,lim=g[u].size();i<lim;i++) if((v=g[u][i].first)!=fa) DFS(v,u,dep+1,value+g[u][i].second),dfs[++m]=u,f[m][0]=u;
}
void init(){
	pow2[0]=1;for(int i=1;i<M;i++) pow2[i]=pow2[i-1]<<1;
	lg2[0]=-1;for(int i=1;i<=m;i++) lg2[i]=lg2[i>>1]+1;
	for(int j=1;j<M;j++) for(int i=1;i<=m;i++) if(i+pow2[j]-1<=m){
		int u=f[i][j-1],v=f[i+pow2[j-1]][j-1];
		if(d[u]<d[v]) f[i][j]=u;else f[i][j]=v;
	}
}
int Dis(int u,int v,int lca=0){
	if(pos[u]<pos[v]) swap(u,v);int lg=lg2[pos[u]-pos[v]+1];
	if(d[f[pos[v]][lg]]<d[f[pos[u]-pow2[lg]+1][lg]]) lca=f[pos[v]][lg];else lca=f[pos[u]-pow2[lg]+1][lg];
	return (LL)val[u]+val[v]-2*val[lca];
}
struct SegmentTree{
	#define lc (o<<1)
	#define rc (o<<1|1)
	#define mid ((l+r)>>1)
	#define Gd(u) Dis(u.first,u.second)
	pr g[N<<2];int d[N<<2];
	pr PushUp(pr u,pr v,int d1=0,int d2=0,int o=0){
		if(!d1 && !d2) d1=Gd(u),d2=Gd(v);
		pr res=d1>d2?u:v;int dd=max(d1,d2);
		if(Dis(u.first,v.first)>dd) res=mpr(u.first,v.first),dd=Gd(res);
		if(Dis(u.first,v.second)>dd) res=mpr(u.first,v.second),dd=Gd(res);
		if(Dis(u.second,v.first)>dd) res=mpr(u.second,v.first),dd=Gd(res);
		if(Dis(u.second,v.second)>dd) res=mpr(u.second,v.second),dd=Gd(res);
		if(o) d[o]=dd;return res;
	}
	void Build(int o,int l,int r){
		if(l==r){ g[o]=mpr(l,l),d[o]=0;return; }
		Build(lc,l,mid);Build(rc,mid+1,r);
		g[o]=PushUp(g[lc],g[rc],d[lc],d[rc],o);
	}
	pr Query(int o,int l,int r,int L,int R){
		if(L<=l && r<=R) return g[o];
		pr res=mpr(L,L);
		if(L<=mid) res=Query(lc,l,mid,L,R);
		if(R>mid) res=PushUp(res,Query(rc,mid+1,r,L,R));
		return res;
	}
	pr Merge(pr u,pr v){
		pr res=mpr(u.first,v.first);int d=Gd(res);
		if(Dis(u.first,v.second)>d) res=mpr(u.first,v.second),d=Gd(res);
		if(Dis(u.second,v.first)>d) res=mpr(u.second,v.first),d=Gd(res);
		if(Dis(u.second,v.second)>d) res=mpr(u.second,v.second),d=Gd(res);
		return res;
	}
	int Query(int a,int b,int c,int d){
		pr r1=Query(1,1,n,a,b),r2=Query(1,1,n,c,d),r3=Merge(r1,r2);
		return Gd(r3);
	}
	#undef lc
	#undef rc
	#undef mid
	#undef Gd
}seg;
int main(){
	n=in();memset(d,0x3f,sizeof(d));
	for(int i=1,u,v,w;i<n;i++) u=in(),v=in(),w=in(),g[u].push_back(mpr(v,w)),g[v].push_back(mpr(u,w));
	DFS(1,1,1,0),init(),seg.Build(1,1,n);
	for(int k=in(),a,b,c,d;k--;){
		a=in(),b=in(),c=in(),d=in();
		printf("%d\n",seg.Query(a,b,c,d));
	}return 0;
}