Cod sursa(job #2871178)

Utilizator SabailaCalinSabaila Calin SabailaCalin Data 12 martie 2022 23:36:16
Problema Algoritmul Bellman-Ford Scor 0
Compilator cpp-64 Status done
Runda Arhiva educationala Marime 1.87 kb
#include <iostream>
#include <fstream>
#include <vector>
#include <queue>

using namespace std;

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

const int SIZE = 50001;
const int INF = 0x3f3f3f3f;

int n, m;

vector <pair <int, int> > G[SIZE];
vector <int> dist(SIZE, INF);

void Read()
{
    f >> n >> m;
    for (int i = 1; i <= n; i++)
    {
        int x, y, z;
        f >> x >> y >> z;
        G[x].push_back(make_pair(y, z));
    }
}

struct Compare
{
    bool operator() (pair <int, int> a, pair <int, int> b)
    {
        return a.second > b.second;
    }
};

bool BellmanFord(int start)
{
    priority_queue <int, vector <pair <int ,int> >, Compare> PQ;
    vector <int> cntInQueue(SIZE, 0);
    vector <bool> onQueue(SIZE, false);

    dist[start] = 0;
    PQ.push(make_pair(start, 0));
    onQueue[start] = true;

    while (PQ.empty() == false)
    {
        int node = PQ.top().first;
        cntInQueue[node]++;
        PQ.pop();
        onQueue[node] = false;

        if (cntInQueue[node] >= n)
        {
            return false;
        }

        for (unsigned int i = 0; i < G[node].size(); i++)
        {
            int neighbour = G[node][i].first;
            int cost = G[node][i].second;

            if (dist[node] + cost < dist[neighbour])
            {
                dist[neighbour] = cost + dist[node];

                if (onQueue[neighbour] == false)
                {
                    PQ.push(make_pair(neighbour, dist[neighbour]));
                    onQueue[neighbour] = true;
                }
            }
        }
    }

    return true;
}

int main()
{
    Read();
    if (BellmanFord(1) == false)
    {
        g << "Ciclu negativ!";
    }
    else
    {
        for (int i = 2; i <= n; i++)
        {
            g << dist[i] << " ";
        }
    }
}