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#pragma GCC optimize(2)
#pragma GCC optimize(3, "Ofast", "inline")
#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef __int128 int128;
namespace FastIO
{
char buf[1 << 20], * p1, * p2;
#define getchar() (p1 == p2 && (p2 = (p1 = buf) + fread(buf, 1, 1 << 20, stdin), p1 == p2) ? EOF : *p1++)
template<typename T> inline T read(T& x) {
x = 0;
int f = 1;
char ch;
while (!isdigit(ch = getchar())) if (ch == '-') f = -1;
while (isdigit(ch)) x = (x << 1) + (x << 3) + (ch ^ 48), ch = getchar();
x *= f;
return x;
}
template<typename T, typename... Args> inline void read(T& x, Args &...x_) {
read(x);
read(x_...);
return;
}
inline ll read() {
ll x;
read(x);
return x;
}
inline void read(char* s) {
scanf("%s", s + 1);
}
};
using namespace FastIO;
const int N = 1e5 + 10;
struct Edge {
int to, nt;
Edge() {}
Edge(int to, int nt) : to(to), nt(nt) {}
}e[N << 1];
int hd[N], cnte;
void AddEdge(int u, int v) {
e[++cnte] = Edge(v, hd[u]);
hd[u] = cnte;
}
int n, m;
pair<int , pair<int , int > >a[N];
inline void Input() {
read(n, m);
int u, v;
for(int i = 1; i < n; i++) {
read(u, v);
AddEdge(u, v);
AddEdge(v, u);
}
for(int i = 1; i <= m; i++) {
read(a[i].second.first, a[i].second.second);
}
}
int dep[N];
int st[N][20];
int vis[N];
inline void Dfs(int u, int fa) {
dep[u] = dep[fa] + 1;
st[u][0] = fa;
for(int i = 1; i < 20; i++) {
st[u][i] = st[st[u][i - 1]][i - 1];
}
for(int i = hd[u]; i; i = e[i].nt) {
int v = e[i].to;
if(v == fa) continue;
Dfs(v, u);
}
}
inline int LCA(int u, int v) {
if(dep[u] < dep[v]) swap(u, v);
for(int i = 19; i >= 0; i--) {
if(dep[st[u][i]] >= dep[v]) {
u = st[u][i];
}
}
if(u == v) return u;
for(int i = 19; i >= 0; i--) {
if(st[u][i] != st[v][i]) {
u = st[u][i], v = st[v][i];
}
}
return st[u][0];
}
inline void Visit(int u) {
vis[u] = 1;
for(int i = hd[u]; i ; i = e[i].nt) {
int v = e[i].to;
if(vis[v] || v == st[u][0]) continue;
Visit(v);
}
}
inline void Work() {
Dfs(1, 0);
for(int i = 1; i <= m; i++) {
a[i].first = LCA(a[i].second.first, a[i].second.second);
cout << a[i].first << ' ' << a[i].second.first << ' ' << a[i].second.second << endl;
}
sort(a + 1, a + m + 1, [](pair<int , pair<int , int > > a, pair<int , pair<int , int > > b) {
return dep[a.first] > dep[b.first];
});
int ans = 0;
for(int i = 1; i <= m; i++) {
if(!vis[a[i].second.first] && !vis[a[i].second.second]){
ans++;
Visit(a[i].first);
}
}
printf("%d", ans);
}
int main() {
int T = 1;
while (T--) {
Input();
Work();
}
return 0;
}
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