TIOJ 1647 to debug

// Knapsack DP is harder than FFT.
#include<bits/stdc++.h>
using namespace std;
typedef long long ll; typedef pair<int,int> pii; typedef pair<ll,ll> pll;
#define ff first
#define ss second
#define pb emplace_back
#define AI(x) begin(x),end(x)
template<class I>bool chmax(I&a,I b){return a<b?(a=b,true):false;}
template<class I>bool chmin(I&a,I b){return b<a?(a=b,true):false;}
#ifdef OWO
#define debug(args...) SDF(#args, args)
#define OIU(args...) ostream& operator<<(ostream&O,args)
#define LKJ(S,B,E,F) template<class...T>OIU(S<T...>s){O<<B;int c=0;for(auto i:s)O<<(c++?", ":"")<<F;return O<<E;}
LKJ(vector,'[',']',i)LKJ(deque,'[',']',i)LKJ(set,'{','}',i)LKJ(multiset,'{','}',i)LKJ(unordered_set,'{','}',i)LKJ(map,'{','}',i.ff<<':'<<i.ss)LKJ(unordered_map,'{','}',i.ff<<':'<<i.ss)
template<class...T>void SDF(const char* s,T...a){int c=sizeof...(T);if(!c){cerr<<"\033[1;32mvoid\033[0m\n";return;}(cerr<<"\033[1;32m("<<s<<") = (",...,(cerr<<a<<(--c?", ":")\033[0m\n")));}
template<class T,size_t N>OIU(array<T,N>a){return O<<vector<T>(AI(a));}template<class...T>OIU(pair<T...>p){return O<<'('<<p.ff<<','<<p.ss<<')';}template<class...T>OIU(tuple<T...>t){return O<<'(',apply([&O](T...s){int c=0;(...,(O<<(c++?", ":"")<<s));},t),O<<')';}
#else
#pragma GCC optimize("Ofast")
#define debug(...) ((void)0)
#endif

const int N = 200002;

int n;
ll k, ans;
vector<pll> adj[N];

bool vis[N];

int siz[N];
void getSize(int u, int p){
    siz[u] = 1;
    for(auto [v, _]: adj[u]){
        if(v == p or vis[v]) continue;
        getSize(v, u);
        siz[u] += siz[v];
    }
}
int getCen(int u, int p, int s){
    for(auto [v, _]: adj[u]){
        if(v == p or vis[v]) continue;
        if(siz[v] * 2 > s) return getCen(v, u, s);
    }
    return u;
}

vector<ll> tmp;
ll sum[N], pmx[N];
void treepre(int u, int p){
    for(auto [v, w]: adj[u]){
        if(v == p or vis[v]) continue;
        sum[v] = sum[u] + w;
        pmx[v] = max(pmx[u], sum[v]);
        treepre(v, u);
    }
}
void dfs(int u, int p){
    tmp.pb(pmx[u]);
    for(auto [v, w]: adj[u]){
        if(v == p or vis[v]) continue;
        dfs(v, u);
    }
}
ll getAns(int u){
    tmp.clear();
    dfs(u, 0);
    sort(AI(tmp));
    ll ret = 0;
    debug(u, tmp);
    for(int i = 0; i < tmp.size(); ++i){
        int j = lower_bound(begin(tmp) + i + 1, end(tmp), k - tmp[i]) - begin(tmp);
        ret += tmp.size() - j;
    }
    debug(u, ret);
    return ret;
}

void cenDecomp(int u, int p){
    getSize(u, p);

    int cen = getCen(u, p, siz[u]);
    debug(cen);
    sum[cen] = pmx[cen] = 0;
    treepre(cen, 0);
    ans += getAns(cen);

    vis[cen] = true;
    for(auto [v, w]: adj[cen]) if(!vis[v]) ans -= getAns(v);
    for(auto [v, _]: adj[cen]) if(!vis[v]) cenDecomp(v, cen);
}

signed main(){
    ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
    cin >> n >> k;
    for(int i = 1, u, v, c; i < n; ++i){
        cin >> u >> v >> c;
        adj[u].pb(v, c);
        adj[v].pb(u, c);
    }

    cenDecomp(1, 0);

    cout << ans;
    return 0;
}