Cod sursa(job #1835597)

Utilizator hantoniusStan Antoniu hantonius Data 27 decembrie 2016 09:22:12
Problema Algoritmul Bellman-Ford Scor 100
Compilator cpp Status done
Runda Arhiva educationala Marime 2.01 kb
//Stan Antoniu
//In acest program folosesc STL prima data, deci va fi un bun suport teoretic.
#include <fstream>
#include <vector>
#include <queue>
#include <bitset>
#include <algorithm>
#include <climits>
#define maxn 50002
using namespace std;

ifstream fin("bellmanford.in");
ofstream fout("bellmanford.out");

vector <pair <int, int> > adj[maxn]; // lista de adiacenta fara pointeri
vector <int> dist(maxn, INT_MAX); //costul minim al unui lant de la 1 la nodul i
vector <int> count_in_queue(maxn, 0); //numara de cate ori un nod a intrat in coada
queue <int> q;
bitset <maxn> in_queue(false); //0 => nodul nu e in coada; 1 => nodul e in coada

int n, m;

void read()
{
    int x, y, c;

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

int main()
{
    int negativ = 0, aux;

    read();
    dist[1] = 0;
    q.push(1);
    in_queue[1].flip(); //echivalent in_queue[1] = true
    while (!q.empty() && !negativ) {
        aux = q.front();
        q.pop();
        in_queue[aux] = false;
        vector < pair <int, int> >::iterator it; //iterator
        for (it = adj[aux].begin(); it != adj[aux].end(); it++) {
            if (dist[aux] < INT_MAX)
                if (dist[it -> first] > dist[aux] + it -> second) {
                    dist[it->first] = dist[aux] + it->second;
                    if (!in_queue[it -> first]) {
                        if (count_in_queue[it -> first] > n) // conditie de ciclu negativ
                            negativ = 1;
                        else {
                            q.push(it -> first);
                            in_queue[it -> first] = true;
                            count_in_queue[it -> first]++;
                        }
                    }
                }
        }
    }
    if (negativ == 1)
        fout << "Ciclu negativ!\n";
    else {
        for (int i = 2; i <= n; i++)
            fout << dist[i] << ' ';
    }
    return 0;
}