2つの特定のノード間にパスが存在するかどうかを確認するC++プログラム

これは、指定された2つのノード間にパスが存在するかどうかを確認するC++プログラムです

アルゴリズム

Begin
   function isReach() is a recursive function to check whether d is reachable to s:
   A) Mark all the vertices as unvisited.
   B) Mark the current node as visited and enqueue it and it will be used to get all adjacent vertices of a vertex.
   C) Dequeue a vertex from queue and print it.
   D) Get all adjacent vertices of the dequeued vertex s.
   E) If an adjacent has not been visited, then mark it visited and enqueue it.
   F) If this adjacent node is the destination node, then return true else continue to BFS.
End

例

#include <iostream>
#include <list>
using namespace std;
class G {
   int n;
   list<int> *adj;
   public:
      G(int n);
      void addEd(int x, int w);
      bool isReach(int s, int d);
};
G::G(int n) { //constructor 
   this->n = n;
   adj = new list<int> [n];
}
void G::addEd(int x, int w) { //adding edge to the graph
   adj[x].push_back(w); //ad w to x’s list
}
bool G::isReach(int s, int d) {
   if (s == d)
   return true;
   bool *visited = new bool[n];
   //Mark all the vertices as unvisited.
   for (int i = 0; i < n; i++)
      visited[i] = false;
   list<int> queue;
   //Mark the current node as visited and enqueue it and it will be used to get all adjacent vertices of a vertex
   visited[s] = true;
   queue.push_back(s);
   list<int>::iterator i;
   while (!queue.empty()) {
      s = queue.front();
      queue.pop_front(); //Dequeue a vertex from queue and print it
      //If a adjacent has not been visited,
      for (i = adj[s].begin(); i != adj[s].end(); ++i) {
         if (*i == d)
            return true;
         if (!visited[*i]) {
            visited[*i] = true;
            queue.push_back(*i);
         }
      }
   }
   return false;
}
int main() {
   G g(4);
   g.addEd(1, 3);
   g.addEd(0, 1);
   g.addEd(2, 3);
   g.addEd(1, 0);
   g.addEd(2, 1);
   g.addEd(3, 1);
   cout << "Enter the source and destination vertices: (0-3)";
   int a, b;
   cin >> a >> b;
   if (g.isReach(a, b))
      cout << "\nThere is a path from " << a << " to " << b;
   else
      cout << "\nThere is no path from " << a << " to " << b;
   int t;
   t = a;
   a = b;
   b= t;
   if (g.isReach(a, b))
      cout << "\nThere is a path from " << a << " to " << b;
   else
      cout << "\nThere is no path from " << a << " to " << b;
   return 0;
}

出力

Enter the source and destination vertices: (0-3)
There is a path from 3 to 1
There is a path from 1 to 3