做不动那么多题了，来个G
G就是问你一棵树能切成多少个大小为3的链，想了半天，想过dp啥的，但是后来发现这个贪心就好了，可以证明贪心找不到的，其他方法也找不到
好久没复健了，这是第一次，感觉以后要多做题才可以
#include <bits/stdc++.h>
using namespace std;
constexpr int limit = (4e5 + 5);//防止溢出
#define INF 0x3f3f3f3f
#define inf 0x3f3f3f3f3f3f3f
#define lowbit(i) i&(-i)//一步两步
#define EPS 1e-9
#define FASTIO ios::sync_with_stdio(false);cin.tie(0),cout.tie(0);
#define pi(a, b) pair<a,b>
#define rep(i, a, b) for(ll i = a; i <= b ; ++i)
#define per(i, a, b) for(ll i = b ; i >= a ; --i)
#define MOD 998244353
#define traverse(u) for(int i = head[u]; ~i ; i = edge[i].next)
#define FOPEN freopen("C:\\Users\\tiany\\CLionProjects\\akioi\\data.txt", "rt", stdin)
#define FOUT freopen("C:\\Users\\tiany\\CLionProjects\\akioi\\dabiao.txt", "wt", stdout)
typedef long long ll;
typedef unsigned long long ull;
char buf[1 << 23], *p1 = buf, *p2 = buf, obuf[1 << 23], *O = obuf;
inline ll read() {
#define getchar() (p1==p2&&(p2=(p1=buf)+fread(buf,1,1<<21,stdin),p1==p2)?EOF:*p1++)
ll sign = 1, x = 0;
char s = getchar();
while (s > '9' || s < '0') {
if (s == '-')sign = -1;
s = getchar();
}
while (s >= '0' && s <= '9') {
x = (x << 3) + (x << 1) + s - '0';
s = getchar();
}
return x * sign;
#undef getchar
}//快读
void print(ll x) {
if (x / 10) print(x / 10);
*O++ = x % 10 + '0';
}
void write(ll x, char c = 't') {
if (x < 0)putchar('-'), x = -x;
print(x);
if (!isalpha(c))*O++ = c;
fwrite(obuf, O - obuf, 1, stdout);
O = obuf;
}
int n,m;
int a[limit];
vector<int>g[limit];
int sizes[limit];
int deg[limit];
void solve() {
cin>>n;
map<pi(int, int), int>mp;
rep(i,1,n)g[i].clear(),sizes[i] = 0, deg[i] = 0;
rep(i,1,n - 1){
int x,y;
cin>>x>>y;
g[x].push_back(y);
g[y].push_back(x);
mp[{x, y}] = i;
mp[{y, x}] = i;
deg[x]++,deg[y]++;
}
if(n <= 2){
cout<<-1<<endl;
return;
}
vector<int>ans;
int ok = 1;
function<void(int, int)> dfs = [&](int u, int fa){
if(!ok)return;
sizes[u] = 1;
for(auto && v : g[u]){
if(v == fa)continue;
dfs(v, u);
sizes[u] += sizes[v];
}
if(sizes[u] == 3){
sizes[u] = 0;// clear all cut
ans.push_back(mp[{fa, u}]);
}else if(sizes[u] > 3){
ok = 0;
return;
}
};
dfs(1, -1);
if(sizes[1] != 0){
cout<<-1<<endl;
return;
}
if(ok){
string oss;
int num = 0;
for(auto && it : ans | std::views::filter([](auto const x) -> bool{return x != 0;})){
oss += to_string(it) + " ";
++num;
}
oss = to_string(num) + "\n" + oss;
cout<<oss<<endl;
}else{
cout<<-1<<endl;
}
}
int32_t main() {
#ifdef LOCAL
FOPEN;
// FOUT;
#endif
FASTIO
int kase;
cin>>kase;
while (kase--)
invoke(solve);
cerr << "Time elapsed: " << 1.0 * clock() / CLOCKS_PER_SEC << "s";
return 0;
}