点分治

请看julao的解释吧，讲的挺清楚的
https://blog.csdn.net/a_forever_dream/article/details/81778649

#include<bits/stdc++.h>
using namespace std;
int n,m,cnt,Size;
struct node{
	int x,y,z,nxt;
}e[20005];
int lnk[10005];
int root,ms,size[10005],mson[10005],sum[10000005],ask[105],ans[105];
bool vis[10005];
inline int read(){
	int ret=0,f=1;char ch=getchar();
	while(ch<'0'||ch>'9'){if(ch='-')f=-f;ch=getchar();}
	while(ch<='9'&&ch>='0')ret=ret*10+ch-'0',ch=getchar();
	return ret*f;
}

void add_e(int x,int y,int z){
	cnt++;e[cnt].x=x;e[cnt].y=y;e[cnt].z=z;e[cnt].nxt=lnk[x];lnk[x]=cnt;
}

void getroot(int x,int fa){
	size[x]=1;mson[x]=0;
	for(int j=lnk[x];j;j=e[j].nxt){
		if(vis[e[j].y]||e[j].y==fa)continue;
		getroot(e[j].y,x);
		size[x]+=size[e[j].y];
		if(size[e[j].y]>mson[x])mson[x]=size[e[j].y];
	}
	if(Size-size[x]>mson[x])mson[x]=Size-size[x];
	if(ms>mson[x])ms=mson[x],root=x;
}

int t;
int dis[10005];
void getdis(int x,int fa,int z){
	dis[++t]=z;
	for(int j=lnk[x];j;j=e[j].nxt){
		if(e[j].y==fa||vis[e[j].y])continue;
		getdis(e[j].y,x,z+e[j].z);
	}
}
struct AS{
	int x,y;
}arr[10005];
int tt;
void solve(int x,int y,int id){
	t=0;
	getdis(x,0,y);
	tt=0;
	sort(dis+1,dis+t+1);
	dis[0]=-1;
	for(int i=1;i<=t;i++)if(dis[i]!=dis[i-1])arr[++tt].x=dis[i],arr[tt].y=1;
	else arr[tt].y++;
	for(int i=1;i<=m;i++){
		if(ask[i]&1==0)
			for(int j=1;j<=tt;j++)
				if(arr[j].x==ask[i]/2)ans[i]+=(arr[j].y-1)*arr[j].y*id;
		for(int j=1;j<=tt&&arr[j].x<ask[i]/2;j++){
			int l=j+1,r=tt;
			while(l<=r){
				int mid=(r-l>>1)+l;
				if(arr[j].x+arr[mid].x==ask[i]){
					ans[i]+=arr[j].y*arr[mid].y*id;
					break;
				}
				if(arr[j].x+arr[mid].x>ask[i])r=mid-1;
				else l=mid+1;
			}
		}
	}
}
void fenzhi(int x,int ssize){
	vis[x]=1;
	solve(x,0,1);
	for(int j=lnk[x];j;j=e[j].nxt){
		if(vis[e[j].y])continue;
		solve(e[j].y,e[j].z,-1);
		ms=1<<30;root=0;
		Size=size[e[j].y]<size[x]?size[e[j].y]:(ssize-size[x]);
		getroot(e[j].y,0);
		fenzhi(root,Size); 
	}
}
int main(){
	freopen("P3806.in","r",stdin);
	freopen("P3806.out","w",stdout);
	n=read();m=read();
	for(int i=1;i<n;i++){
		int x,y,z;
		x=read(),y=read(),z=read();
		add_e(x,y,z);add_e(y,x,z);
	}
	for(int i=1;i<=m;i++)ask[i]=read();
	root=0;ms=1<<30;Size=n;
	getroot(1,0);
	fenzhi(root,n);
	for(int i=1;i<=m;i++)
	if(ans[i]>0)printf("AYE
"); 
	else printf("NAY
");
	return 0; 
}