Дейкстра

#include<iostream>
#include<fstream>
#include<vector>

using namespace std;
int inf = 1000000;

int main() {

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

    int n, st, fn;
    fin >> n >> st >> fn;
    --st; --fn;
    vector<vector<int>> mas(n, vector<int>(n));
    for (int i = 0; i < n; ++i) {
        for (int j = 0; j < n; ++j) {
            fin >> mas[i][j];
        }
    }
    pair<bool, int> temp;
    temp.first = false; temp.second = inf;
    vector<pair<bool, int>> w(n, temp);
    w[st].second = 0;
    int v = st;

    for (int i = 0; i < mas.size(); ++i) {
        int minimal = inf;
        for (int j = 0; j < mas.size(); ++j) {
            if (!w[j].first && w[j].second <= minimal) {
                minimal = w[j].second;
                v = j;
            }
        }
        w[v].first = true;
        for (int j = 0; j < mas.size(); ++j) {
            if (mas[v][j] != -1)
                w[j].second = min(w[j].second, w[v].second + mas[v][j]);
        }
    }

    if (w[fn].second == inf) {
        fout << -1 << endl;
        return 0;
    }

    fout << w[fn].second << endl;
    return 0;
}