4 контест 2 задача

#include <iostream>
#include<vector>
#include<algorithm>
#include <iomanip>

using namespace std;

vector<vector<pair<int, int>>> G;
vector<int> used;
vector<int> dist;
vector<int> parents;
int n;

void dkstr(int v) {
    dist[v] = 0;
    for (int i = 0; i < n; i++) {
        //поиск минимума
        int min_v = -1;
        int min_dist = 1000000000;
        for (int i = 0; i < n; i++) {
            if (used[i] == 0 && dist[i] < min_dist) {
                min_v = i;
                min_dist = dist[i];
            }
        }
        if (min_v == -1) {
            return;
        }
        //релаксация
        used[min_v] = 1;
        for (int i = 0; i < G[min_v].size(); i++) {
            int actual_v = G[min_v][i].first;
            int weight = G[min_v][i].second;
            if (used[actual_v] == 0 && dist[actual_v] > min_dist + weight) {
                dist[actual_v] = min_dist + weight;
                parents[actual_v] = min_v;
            }
        }
    }
}

int main() {
    int s, f;
    cin >> n >> s >> f;
    s -= 1;
    f -= 1;

    G = vector<vector<pair<int, int>>>(n);
    used = vector<int>(n);
    dist = vector<int>(n, 1000000000);
    parents = vector<int>(n, -1);

    //ввод данных
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++) {
            int a;
            cin >> a;
            if (a != 0 && a != -1) {
                G[i].push_back(make_pair(j, a));
            }
        }
    }

    dkstr(s);
    if (used[f] == 0) {
        cout << -1;
    } else {
        // f - > s
        vector<int> ans;
        while (f != -1){
            ans.push_back(f);
            f = parents[f];
        }

        for (int i = ans.size() - 1; i >= 0; i--){
            cout << ans[i] + 1 << ' ';
        }
    }
    return 0;
}