G8: SST for sparse graph

#include <iostream>
#include <fstream>
#include <vector>
#include <set>
#include <queue>

#define INF 100000001

using namespace std;
int n;

void dfs(vector<vector<pair<int, int>>> &g, vector<bool> &visited, int v) {
    visited[v] = true;
    for (int i = 0; i < g[v].size(); i++)
        if (!visited[g[v][i].first])
            dfs(g, visited, g[v][i].first);
}


void Prima(vector<vector<pair<int, int>>> &g, ofstream &fout) {
    vector<bool> visited(n, false);
    vector<int> min(n, INF);
    min[0] = 0;
    set<pair<int, int>> q;
    int count = 0;
    q.insert(pair<int, int>(0, 0));
    while (!q.empty()) {
        int v = q.begin()->second;
        q.erase(q.begin());
        for (int j = 0; j < g[v].size(); j++) {
            if (!visited[g[v][j].first] && g[v][j].second < min[g[v][j].first]) {
                q.erase(pair<int, int>(min[g[v][j].first], g[v][j].first));
                min[g[v][j].first] = g[v][j].second;
                q.insert(pair<int, int>(min[g[v][j].first], g[v][j].first));
            }

        }
        visited[v] = true;
        count += min[v];
    }
    fout << count;
}

int main() {

    ifstream fin("input.txt");
    ofstream fout("output.txt");

    int m;
    fin >> n >> m;
    vector<vector<pair<int, int>>> g(n);

    int tmpV1, tmpV2, weight;

    for (int i = 0; i < m; i++) {
        fin >> tmpV1 >> tmpV2 >> weight;
        g[tmpV1 - 1].push_back(pair<int, int>(tmpV2 - 1, weight));
        g[tmpV2 - 1].push_back(pair<int, int>(tmpV1 - 1, weight));
    }

    vector<bool> visited(n, false);
    dfs(g, visited, 0);
    for (int i = 0; i < visited.size(); i++) {
        if (!visited[i]) {
            fout << -1;
            return 0;
        }
    }
    Prima(g, fout);

    fin.close();
    fout.close();
    return 0;
}