12.2.3. Цикл

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

struct edge
{
    int from, to, cost;
};
const int INF = 1e9;;

int main(){
    int n;
    cin >> n;
    vector <edge> E;
    for (int i = 0; i < n; i++)
    {
        for (int j = 0; j < n; j++)
        {
            int x;
            cin >> x;
            if (x != 0 && x != 100000){
                E.push_back({ i, j, x });
            }
        }
    }
    int x;
    vector<int> d(n, INF), p(n, -1);
    d[0] = 0;
    for (int i = 0; i < n; i++)
    {
        x = -1;
        for (int j = 0; j < E.size(); j++)
        {
            int from = E[j].from;
            int to = E[j].to;
            int cost = E[j].cost;
            if (d[to] > d[from] + cost)
            {
                d[to] = max(d[from] + cost, -INF);
                p[to] = from;
                x = to;
            }
        }
    }
    if (x == -1)
    {
        cout << "NO" << endl;
    }
    else{
        int y = x;
        for (int i = 0; i < n; i++)
        {
            y = p[y];
        }
        vector <int> path;
        for (int cur = y;; cur = p[cur])
        {
            path.push_back(cur);
            if (cur == y && path.size() > 1)
            {
                break;
            }
        }
        reverse(path.begin(), path.end());
        cout << "YES" << endl;
        cout << path.size() << endl;
        for (int i = 0; i < path.size(); i++)
        {
            cout << path[i] + 1;
            if (i != path.size() - 1)
            {
                cout << ' ';
            }
        }
        cout << endl;
    }
    system("pause");
    return 0;
}