Cod sursa(job #3229712)

Utilizator dorin.ileailea dorin dorin.ilea Data 17 mai 2024 10:07:09
Problema BFS - Parcurgere in latime Scor 100
Compilator cpp-64 Status done
Runda Arhiva educationala Marime 2.64 kb
#include <bits/stdc++.h>
using namespace std;

class Task {
 public:
  void solve() {
    read_input();
    print_output(get_result());
  }

 private:
  // numarul maxim de noduri
  static constexpr int NMAX = (int)1e5 + 5;  // 10^5 + 5 = 100.005

  // n = numar de noduri, m = numar de muchii/arce
  int n, m;

  // adj[node] = lista de adiacenta a nodului node
  // exemplu: daca adj[node] = {..., neigh, ...} => exista muchia (node, neigh)
  vector<int> adj[NMAX];

  // nodul sursa in parcurgerea BFS
  int source;

  void read_input() {
    ifstream fin("bfs.in");
    fin >> n >> m >> source;
    for (int i = 1, x, y; i <= m; i++) {
      fin >> x >> y;  // muchie (x, y)
      adj[x].push_back(y);
      // orientat
      // adj[y].push_back(x);
    }

    fin.close();
  }
  void bfs(int source, vector<int>& d, vector<int>& parents,
           vector<int>& visited) {
    queue<int> q;
    d[source] = 0;
    parents[source] = -1;
    q.push(source);
    // color the node
    visited[source] = 1;

    while (!q.empty()) {
      int node = q.front();
      q.pop();
      //  use node here!
      for (auto& neigh : adj[node]) {
        if (visited[neigh] == 0) {  // not yet visited
          d[neigh] = d[node] + 1;
          parents[neigh] = node;
          visited[neigh] = 1;
          q.push(neigh);
        }
      }
      visited[node] = 2;
    }
  }

  vector<int> get_result() {
    // TODO: Faceti un BFS care sa construiasca in d valorile cerute:
    // * d[node] = numarul minim de muchii de parcurs de la nodul `source` la
    // nodul `node`
    //      * d[source] = 0
    //      * d[node]   = -1, daca nu exista drum de la source la node
    // *******
    // ATENTIE: nodurile sunt indexate de la 1 la n.
    // *******

    vector<int> d(n + 1);
    // add by me:
    vector<int> parents(n + 1);
    vector<int> visited(n + 1);
    for (int i = 1; i <= n; i++) {
      d[i] = -1;
      parents[i] = -1;
      visited[i] = 0;
    }
    bfs(source, d, parents, visited);
    return d;
  }

  void print_output(const vector<int>& d) {
    ofstream fout("bfs.out");
    for (int node = 1; node <= n; node++) {
      fout << d[node] << (node == n ? '\n' : ' ');
    }
    fout.close();
  }
};

// [ATENTIE] NU modifica functia main!
int main() {
  // * se aloca un obiect Task pe heap
  // (se presupune ca e prea mare pentru a fi alocat pe stiva)
  // * se apeleaza metoda solve()
  // (citire, rezolvare, printare)
  // * se distruge obiectul si se elibereaza memoria
  auto* task = new (nothrow) Task();  // hint: cppreference/nothrow
  if (!task) {
    cerr << "new failed: WTF are you doing? Throw your PC!\n";
    return -1;
  }
  task->solve();
  delete task;
  return 0;
}