这是我的代码：

#include <cstdio>
#include <iostream>
#include <algorithm>
#include <cstring>
using namespace std;

const int N=10005;
const int M=20005;

int n,k;
int e[M],ne[M],w[M],h[N],tot;
int del[N];
int arr1[N],idx1,arr2[N],idx2;

inline void add(int a,int b,int c) {
    e[tot]=b,w[tot]=c,ne[tot]=h[a],h[a]=tot++;
}

inline int get_size(int u,int fa) {
    if (del[u]) return 0;
    int sz=0;
    for (int i=h[u];~i;i=ne[i]) {
        if (e[i]==fa) continue;
        sz+=get_size(e[i],u);
    }
    return sz;
}

inline int get_center(int u,int fa,int sz,int& cen) {
    if (del[u]) return 0;
    int mx=0;
    int sum=1;
    for (int i=h[u];~i;i=ne[i]) {
        if (e[i]==fa) continue;
        int k=get_center(e[i],u,sz,cen);
        sum+=k;
        mx=max(mx,k);
    }
    mx=max(mx,sz-sum);
    if (mx<=sz/2) cen=u;
    return sum;
}

inline void get_dis(int u,int fa,int dis,int& idx) {
    if (del[u]) return;
    arr2[++idx]=dis;
    for (int i=h[u];~i;i=ne[i]) {
        if (e[i]==fa) continue;
        get_dis(e[i],u,dis+w[i],idx);
    }
}

bool cmp(const int& a,const int& b) {
    return a<b;
}

inline int calc(int* arr,int idx) {
    int res=0;
    sort(arr+1,arr+1+idx,cmp);
    for (int i=0,j=idx;j;--j) {
        while (i+1<j && arr[i+1]+arr[j]<=k) i++;
        i=min(i,j-1);
        res+=i-1;
    }
    return res;
}

inline int solve(int u) {
    if (del[u]) return 0;
    get_center(u,0,get_size(u,0),u);
    del[u]=true;
    int res=0;
    idx1=0;
    for (int i=h[u];~i;i=ne[i]) {
        idx2=0; get_dis(e[i],u,w[i],idx2);
        res-=calc(arr2,idx2);
        for (int j=1;j<=idx2;++j) {
            if (arr2[j]<=k) res++;
            arr1[++idx1]=arr2[j];
        }
    }
    res+=calc(arr1,idx1);
    for (int i=h[u];~i;i=ne[i]) res+=solve(e[i]);
    return res;
}

int main() {
    while (scanf("%d %d",&n,&k),n || k) {
        for (int i=1;i<=n;++i) del[i]=false,h[i]=-1;
        for (int i=1;i<=n-1;++i) {
            int a,b,c;
            scanf("%d %d %d",&a,&b,&c); a++,b++;
            add(a,b,c); add(b,a,c);
        }
        printf("%d\n",solve(1));
    }
    return 0;
}

这是另外一份代码：

#include <iostream>
#include <cstring>
#include <algorithm>

using namespace std;

const int N = 10010, M = N * 2;

int n, m;
int h[N], e[M], w[M], ne[M], idx;
bool st[N];
int p[N], q[N];

void add(int a, int b, int c)
{
    e[idx] = b, w[idx] = c, ne[idx] = h[a], h[a] = idx ++ ;
}

int get_size(int u, int fa)  // 求子树大小
{
    if (st[u]) return 0;
    int res = 1;
    for (int i = h[u]; ~i; i = ne[i])
        if (e[i] != fa)
            res += get_size(e[i], u);
    return res;
}

int get_wc(int u, int fa, int tot, int& wc)  // 求重心
{
    if (st[u]) return 0;
    int sum = 1, ms = 0;
    for (int i = h[u]; ~i; i = ne[i])
    {
        int j = e[i];
        if (j == fa) continue;
        int t = get_wc(j, u, tot, wc);
        ms = max(ms, t);
        sum += t;
    }
    ms = max(ms, tot - sum);
    if (ms <= tot / 2) wc = u;
    return sum;
}

void get_dist(int u, int fa, int dist, int& qt)
{
    if (st[u]) return;
    q[qt ++ ] = dist;
    for (int i = h[u]; ~i; i = ne[i])
        if (e[i] != fa)
            get_dist(e[i], u, dist + w[i], qt);
}

int get(int a[], int k)
{
    sort(a, a + k);
    int res = 0;
    for (int i = k - 1, j = -1; i >= 0; i -- )
    {
        while (j + 1 < i && a[j + 1] + a[i] <= m) j ++ ;
        j = min(j, i - 1);
        res += j + 1;
    }
    return res;
}

int calc(int u)
{
    if (st[u]) return 0;
    int res = 0;
    get_wc(u, -1, get_size(u, -1), u);
    st[u] = true;  // 删除重心

    int pt = 0;
    for (int i = h[u]; ~i; i = ne[i])
    {
        int j = e[i], qt = 0;
        get_dist(j, -1, w[i], qt);
        res -= get(q, qt);
        for (int k = 0; k < qt; k ++ )
        {
            if (q[k] <= m) res ++ ;
            p[pt ++ ] = q[k];
        }
    }
    res += get(p, pt);

    for (int i = h[u]; ~i; i = ne[i]) res += calc(e[i]);
    return res;
}

int main()
{
    while (scanf("%d%d", &n, &m), n || m)
    {
        memset(st, 0, sizeof st);
        memset(h, -1, sizeof h);
        idx = 0;
        for (int i = 0; i < n - 1; i ++ )
        {
            int a, b, c;
            scanf("%d%d%d", &a, &b, &c);
            add(a, b, c), add(b, a, c);
        }

        printf("%d\n", calc(0));
    }

    return 0;
}

为什么我这份 TLE 了，他那份 AC 了，我看着好像没啥问题呀。