`板子题`` #include using namespace std; using ll = long long; const int N = 1e6 + 9; struct node{ ll u,v,w; bool operator < (const node &a) const{ if(w!=a.w) return w<a.w; else if(v!=a.v) return v<a.v; else return u<a.u; } }; ll fa[N]; ll root(int x){ return fa[x] = (fa[x] == x ? x : root(fa[x])); } vector<node> es; signed main(){ ios::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL); ll n,m;cin>>n>>m; for(int i=1;i<=m;i++){ ll u,v,w;cin>>u>>v>>w; es.push_back({u,v,w}); } ll ans = 0; sort(es.begin(),es.end()); for(int i=1;i<=n;i++) fa[i] = i;

for(auto &y : es){
	if(root(y.u)==root(y.v)) continue;
	ans += y.w;
	fa[root(y.v)] = root(y.u);
}

for(int i = 1; i < n; i++) if(root(i) != root(i + 1)) ans = -1; if(ans!=-1) cout << ans << "\n"; else cout<<"impossible"; }