Shared code

#include<bits/stdc++.h>
#define int long long

using namespace std;

const int INF = 1e9;

vector<pair<int,int>> adj[100005];
int visited[100005];
int cost = 0;
vector<int> dist(100005,INF);


void dfs(int node){
     visited[node] = 1;
     for(auto it: adj[node]){
        if(visited[it.first]==0){
            dfs(it.first);
        }
     }
}

void prismmsp(int node){
      dist[node] = 0;
      set<pair<int,int>> s;
      s.insert({0,node});
      while(!s.empty()){
        auto x = *(s.begin());
        s.erase(x);
        int u = x.second;
        int w = x.first;
        cost += w;
        visited[u] = 1;
        for(auto it: adj[u]){
            if(visited[it.first]==1){
                continue;
            }
            if(dist[it.first]>it.second){
                s.erase({dist[it.first],it.first});
                dist[it.first] = it.second;
                s.insert({dist[it.first],it.first});
            }
        }

      }
}



signed main(){
    int n,m;cin>>n>>m;
    int a,b,c;
    for(int i=0;i<m;i++){
        cin>>a>>b>>c;
        adj[a].push_back({b,c});
        adj[b].push_back({a,c});
    }
    int ct=0;
    for(int i=1;i<=n;i++){
        if(visited[i]==0){
            ct++;
            dfs(i);
        }
    }
    if(ct>1){
        cout<<"IMPOSSIBLE"<<"\n";
        return 0;
    }
    memset(visited,0,sizeof(visited));
    prismmsp(1);
    cout<<cost<<"\n";

}