Shared code

#include <bits/stdc++.h>
#define uwu return 0;

using namespace std;

const int SIZE = 1e5 + 5;

const long long INF = 1e18 + 7;

struct edge{
    int u, v, id;
    long long w;
    edge(int _u, int _v, int _id, long long _w) : u(_u), v(_v), id(_id), w(_w) {};
};

vector<edge> graph[SIZE];

vector <int> forest[SIZE];

int cc[SIZE];

bool been[2 * SIZE];

edge min_edge(edge e1, edge e2){
    if(e1.w == e2.w)
        return (e1.id < e2.id ? e1 : e2);
    return (e1.w < e2.w ? e1 : e2);
}

int cc_ptr = 0;

void set_cc(int nd, int rt){
    cc[nd] = cc_ptr;
    for(auto i:forest[nd]){
        if(i != rt)
            set_cc(i, nd);
    }
    return;
}

edge find_safe_edge(int nd, int rt){
    edge ret(nd, 0, 0, INF);
    for(auto i:graph[nd]){
        if(cc[nd] != cc[i.v])
            ret = min_edge(ret, i);
    }
    for(auto i:forest[nd]){
        if(i != rt)
            ret = min_edge(ret, find_safe_edge(i, nd));
    }
    return ret;
}

long long Boruvka(int V){
    for (int i = 1; i <= V; i++){
        cc[i] = 0;
    }
    cc_ptr = 0;
    vector <edge> edge_vec;
    for (int i = 1; i <= V; i++){
        if(!cc[i]){
            cc_ptr++;
            set_cc(i, 0);
            edge_vec.push_back(find_safe_edge(i, 0));
        }
    }
    if(cc_ptr == 1)
        return 0;
    long long sum_w = 0;
    for(auto i:edge_vec){
        if(!been[i.id]){
            forest[i.u].push_back(i.v);
            forest[i.v].push_back(i.u);
            been[i.id] = 1;
            sum_w += i.w;
        }
    }
    return sum_w;
}

int main(){
    int V, E;
    cin >> V >> E;
    for (int u, v, w, i = 1; i <= E; i++){
        cin >> u >> v >> w;
        edge eu(u, v, i, w), ev(v, u, i, w);
        graph[u].push_back(eu);
        graph[v].push_back(ev);
    }
    long long ans = 0;
    for (int i = 0; i <= __lg(V); i++){
        ans += Boruvka(V);
        if(ans > INF)
            break;
    }
    if(ans < INF)
        cout << ans << '\n';
    else
        cout << "IMPOSSIBLE\n";
    uwu
}