本人用了完全不对的点分治过了本题，错误的点在代码中标出来了：

hack:

input

10 30
5 2 2
5 9 6
2 1 6
2 4 5
9 7 9
9 10 9
4 3 3
7 6 10
7 8 6

output

41

wrong code:

#include <iostream>
#include <iomanip>
#include <vector>
#include <stack>
#include <queue>
#include <bitset>
#include <map>
#include <set>
#include <unordered_map>
#include <unordered_set>
#include <cstring>
#include <sstream>
#include <algorithm>
#include <cmath>
#include <ctime>
#include <cassert>
#define x first
#define y second
#define pb push_back
#define eb emplace_back
#define pf push_front
#define desktop "C:\\Users\\MPC\\Desktop\\"
using namespace std;
typedef long long LL;
typedef unsigned long long ULL;
typedef pair <int,int> PII;
const int dx[] = {1,0,-1,0},dy[] = {0,-1,0,1};
template <typename T1,typename T2> bool tomax (T1 &x,T2 y) {
	if (y > x) return x = y,true;
	return false;
}
template <typename T1,typename T2> bool tomin (T1 &x,T2 y) {
	if (y < x) return x = y,true;
	return false;
}
LL power (LL a,LL b,LL p) {
	LL ans = 1;
	while (b) {
		if (b & 1) ans = ans * a % p;
		a = a * a % p;
		b >>= 1;
	}
	return ans;
}
const int N = 40010;
int n,m;
vector <PII> g[N];
bool del[N];
int s[N];
int p[N],q[N];
int center;
int lp,lq;
void get_size (int u,int fa) {
	if (del[u]) return ;
	s[u] = 1;
	for (auto [v,w] : g[u]) {
		if (v == fa) continue;
		get_size (v,u);
		s[u] += s[v];
	}
}
void get_center (int u,int fa,int tot) {
	if (del[u]) return ;
	int maxx = 0;
	for (auto [v,w] : g[u]) {
		if (v == fa) continue;	//没有到下一层找重心
		tomax (maxx,s[v]);
	}
	tomax (maxx,tot - s[u]);
	if (maxx <= tot) center = u;	//重心的定义错了
}
void get_dist (int u,int fa,int dist) {
	if (del[u]) return ;
	q[++lq] = dist;
	for (auto [v,w] : g[u]) {
		if (v == fa) continue;
		get_dist (v,u,dist + w);
	}
}
int calc (int n,int a[]) {
	sort (a + 1,a + n + 1);
	int ans = 0;
	for (int i = n,j = 0;i >= 1;i--) {
		while (j + 1 < i && a[j + 1] + a[i] <= m) j++;
		tomin (j,i - 1);
		ans += j;
	}
	return ans;
}
int solve (int u) {
	get_size (u,-1);
	center = -1;
	get_center (u,-1,s[u]);
	u = center;
	del[u] = true;
	int ans = 0;
	lp = 0;
	for (auto [v,w] : g[u]) {
		lq = 0;
		get_dist (v,-1,w);
		ans -= calc (lq,q);
		for (int i = 1;i <= lq;i++) {
			if (q[i] <= m) ans++;
			p[++lp] = q[i];
		}
	}
	ans += calc (lp,p);
	for (auto [v,w] : g[u]) ans += solve (v);
	return ans;
}
int main () {
	cin >> n;
	for (int i = 1;i <= n - 1;i++) {
		int a,b,w;
		cin >> a >> b >> w;
		g[a].pb ({b,w}),g[b].pb ({a,w});
	}
	cin >> m;
	cout << solve (1) << endl;
	return 0;
}