Cod sursa(job #3333764)

Utilizator repzcuOprescu Andrei repzcu Data 15 ianuarie 2026 03:12:35
Problema Algoritmul Bellman-Ford Scor 100
Compilator cpp-64 Status done
Runda Arhiva educationala Marime 2.24 kb
#include <fstream>
#include <vector>
#include <queue>
#include <climits>
using namespace std;

ifstream f("bellmanford.in");
ofstream g("bellmanford.out");

int main()
{
    int n, m;
    f >> n >> m;

    // Lista de adiacenta: adj[nod] = vector de (vecin, cost)
    vector<vector<pair<int, int>>> adj(n + 1);

    for (int i = 0; i < m; i++)
    {
        int x, y, c;
        f >> x >> y >> c;
        adj[x].push_back({y, c});
    }

    // dist[i] = distanta minima de la nodul 1 la nodul i
    vector<long long> dist(n + 1, LLONG_MAX);
    dist[1] = 0;

    // cnt[i] = de cate ori a fost adaugat nodul i in coada
    vector<int> cnt(n + 1, 0);

    // inQueue[i] = true daca nodul i este in coada
    vector<bool> inQueue(n + 1, false);

    // SPFA (Shortest Path Faster Algorithm) - optimizare Bellman-Ford
    queue<int> q;
    q.push(1);
    inQueue[1] = true;
    cnt[1] = 1;

    bool cicluNegativ = false;

    while (!q.empty() && !cicluNegativ)
    {
        int nod = q.front();
        q.pop();
        inQueue[nod] = false;

        for (auto &muchie : adj[nod])
        {
            int vecin = muchie.first;
            int cost = muchie.second;

            if (dist[nod] != LLONG_MAX && dist[nod] + cost < dist[vecin])
            {
                dist[vecin] = dist[nod] + cost;

                if (!inQueue[vecin])
                {
                    q.push(vecin);
                    inQueue[vecin] = true;
                    cnt[vecin]++;

                    // Daca un nod a fost adaugat de mai mult de N ori,
                    // exista un ciclu negativ
                    if (cnt[vecin] > n)
                    {
                        cicluNegativ = true;
                        break;
                    }
                }
            }
        }
    }

    if (cicluNegativ)
    {
        g << "Ciclu negativ!\n";
    }
    else
    {
        for (int i = 2; i <= n; i++)
        {
            if (dist[i] == LLONG_MAX)
                g << 0; // Nu exista drum (conform problemei de la Dijkstra)
            else
                g << dist[i];

            if (i < n)
                g << " ";
        }
        g << "\n";
    }

    return 0;
}