树分治模板

#include <cstdio>
#include <algorithm>
#include <vector>
#include <cmath>
#pragma comment(linker,"/STACK:102400000,102400000")
using namespace std;

#define MP make_pair
#define PB push_back
typedef long long LL;
typedef pair<int,int> PII;
const double eps=1e-8;
const double pi=acos(-1.0);
const int K=1e5+7;
const int mod=1e9+7;

vector<PII >mp[K];
int cnt,ans,vis[K],tdis[K],dis[K];
struct CenterTree
{
    int n,ret,mx,son[K];
    void dfs(int x,int f)
    {
        son[x]=1;
        int tmp=0;
        for(int i=0;i<mp[x].size();i++)
        if(f!=mp[x][i].first && !vis[mp[x][i].first])
        {
            dfs(mp[x][i].first,x);
            son[x]+=son[mp[x][i].first];
            tmp=max(tmp,son[mp[x][i].first]);
        }
        tmp=max(tmp,n-son[x]);
        if(tmp<mx)
            mx=tmp,ret=x;
    }
    int getCenter(int x,int num)
    {
        n=num,mx=0x3f3f3f3f;
        dfs(x,0);
        return ret;
    }
}center;
void getArray(int x,int f)
{
    tdis[++cnt]=dis[x];
    for(int i=0;i<mp[x].size();i++)
    if(mp[x][i].first!=f && !vis[mp[x][i].first])
    {
        dis[mp[x][i].first]=dis[x]+mp[x][i].second;
        getArray(mp[x][i].first,x);
    }
}
int calc(int x,int d,int mx)
{
    dis[x]=d,cnt=0;
    getArray(x,0);
    sort(tdis+1,tdis+1+cnt);
    int ret=0,l=1,r=cnt;
    while(l<r)
        if(tdis[l]+tdis[r]<=mx) ret+=r-l,l++;
        else r--;
    return ret;
}
void solve(int x,int mx)
{
    ans+=calc(x,0,mx);
    vis[x]=1;
    for(int i=0;i<mp[x].size();i++)
    if(!vis[mp[x][i].first])
    {
        ans-=calc(mp[x][i].first,mp[x][i].second,mx);
        solve(center.getCenter(mp[x][i].first,center.son[mp[x][i].first]),mx);
    }
}
int main(void)
{
    int n,mx;
    while(~scanf("%d%d",&n,&mx)&&n)
    {
        for(int i=1;i<=n;i++)
            mp[i].clear(),vis[i]=0;
        for(int i=1,x,y,z;i<n;i++)
            scanf("%d%d%d",&x,&y,&z),mp[x].PB(MP(y,z)),mp[y].PB(MP(x,z));
        ans=0;
        solve(center.getCenter(1,n),mx);
        printf("%d
",ans);
    }
    return 0;
}