Cod sursa(job #1849238)

Utilizator alex99Chelba Alexandru alex99 Data 17 ianuarie 2017 10:35:03
Problema Algoritmul Bellman-Ford Scor 0
Compilator cpp Status done
Runda Arhiva educationala Marime 2.1 kb
#include <fstream>
#include <vector>
#include <algorithm>
#include <queue>
using namespace std;

const int maxv=20000000;//infinit
const int maxn=50002;//numarul de varfuri

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

struct vecin{
    int j;//succesorul
    int c;//costul
};

int d[maxn];//distantele minime
vector <vecin> V[maxn];//listele vecinilor
int p[maxn];//time minte de cate ori s-a folosit fiecare nod
int t[maxn];//tata
int n,m;
queue <int> q;//coada pt parcurgerea nodurilor (asemanantor BF)

void citire()
{
    fin>>n>>m;
    for(int i=1;i<=m;i++)
    {
        vecin y;
        int x;
        fin>>x>>y.j>>y.c;
        V[x].push_back(y);
    }
}

void drum(int i)
{ if(t[i]) drum(t[i]);
  fout<<i<<" ";
}

int belmanFord (int s)
{
    for(int i=1; i<=n; i++) d[i]=maxv;//initializez cu infinit distantele
    d[s]=0;//distanta la nodl de start
    t[s]=0;//tata de start
    q.push(s);//pun in coada
    int k;
    while(!q.empty())// sau q.size()!=0  - cat timp coada nu e vida
    {
        k=q.front();//primul din coada
        q.pop();//scot primul din coada
        p[k]++;//l-am folosit inca o data
        if(p[k]==n) return 1;//ciclu negativ
        for(int i=0;i<V[k].size();i++)//parcurg vecinii
        {
            if (d[V[k][i].j]>d[k]+V[k][i].c)//drum mai scurt prin k
            {
                d[V[k][i].j]=d[k]+V[k][i].c;//imbunatatesc distanta
                q.push(V[k][i].j);//adaug in coada vecinul
                t[V[k][i].j]=k;//k e tata celui spre care am imbunatatit
            }
        }
    }
    return 0;
}

void afis()
{
    for(int i=1;i<=n;i++)
        if(d[i]!=maxv) fout<<d[i]<<" ";
        else fout<<"- ";
    fout<<"\n";
}

int main()
{
    int s;
    citire();
    fin>>s;
    if(belmanFord(s)==0)
    {
        afis();
        for(int i=1;i<=n;i++)
        {   fout<<s<<"->"<<i<<":";
            if(t[i]) drum(i);
            else fout<<"-";
            fout<<endl;
        }
    }
    else fout<<"Ciclu negativ!\n";
    fin.close();
    fout.close();
    return 0;
}