Cod sursa(job #2928789)

Utilizator Alin_2205Alin Pop Alin_2205 Data 23 octombrie 2022 21:27:59
Problema Algoritmul lui Dijkstra Scor 20
Compilator cpp-64 Status done
Runda Arhiva educationala Marime 1.71 kb
#include <fstream>
#include <iostream>
#include <vector>
#include <queue>
#include <algorithm>
#include <tuple>
using namespace std;

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

const int Inf = (1 << 30);
using PI  = pair<int, int>;
using VP  = vector<PI>;
using VVP = vector<VP>;
using VI = vector<int>;

VVP G;   // graf-ul 
VI d;    // vectorul de distante

int n, m; // nr de noduri & muchii

void ReadGraph();
void Dijkstra(int x, VI& d);  // neaparat referinta!!
void WriteDistances();

int main()
{
    ReadGraph();
    Dijkstra(1, d);
    WriteDistances();
}

void ReadGraph()
{
    fin >> n >> m;
    G = VVP(n + 1);
    int x, y, w; // w = costul muchiei
    while (m--)
    {
        fin >> x >> y >> w;
        G[x].emplace_back(y, w);
        G[y].emplace_back(x, w); // G.N.
    }
}

void Dijkstra(int x, VI& d)
{
    priority_queue<PI, vector<PI>, greater<PI>> Q;
    d = VI(n + 1, Inf);
    d[x] = 0;        // distanta de la sursa la ea insasi este 0 (x -> sursa);
    Q.emplace(0, x); // trimit in coada distanta si nodul sursa
    
    int dx, y, w;
    while (!Q.empty())
    {
        tie(dx, x) = Q.top();
        Q.pop();

        if (dx > d[x]) // daca x a fost plasat anterior in coada
           continue;  

        for (auto pos : G[x])
        {
            tie(y, w) = pos;
            if (d[y] > d[x] + w) // daca scade nr. de pasi pana la nodul y
            {   
                d[y] = d[x] + w;
                Q.emplace(d[y], y);
            }
        }
    }
}

void WriteDistances()
{
    for (int i = 2; i <= n; ++i)
        if (d[i] != Inf)
           fout << d[i] << " ";
        else
           fout << 0 << " ";
}