如何使用邻接矩阵计算孤立顶点的数量

Question

I've got stuck with the problem of counting amount of isolated vertices in the graph. Below you will see the code

#include <iostream>
#include <vector>
#define V 4 // amount of vertices in the graph 
// Function to add edge between vertices
void addEdge(std::vector<int> adj[V], int u, int v)
{
   adj[u].push_back(v);
   adj[v].push_back(u);
}
// Function to count amount of isolated vertices in graph with return type int
int FindIsolated(std::vector<int> adj[V])
{
   int isolated = 0; // counter to save amount of isolated vertices
   for(int v = 0; v < V; ++v)
   {
      for(auto x: adj[v])
      {
         if(x == 0)
         {
            isolated++;
         }
      }
   }
    return isolated;
}
// Driver code
int main()
{
   std::vector<int> adj[V];
   addEdge(adj, 1, 2);
   addEdge(adj, 1, 3);
   addEdge(adj, 0, 0);
   std::cout << "This graph contains " << FindIsolated(adj) << " isolated vertices" << std::endl;
   std::cin.get();
   return 0;
}

In the output I have a message: "This graph contains 2 isolated vertices" but I need the message "This graph contains 1 isolated vertices" Any suggestions and describing the solution is appreciated. Thank you :)

Answer 1

void addEdge(std::vector<int> adj[V], int u, int v)
{
   adj[u].push_back(v);
   adj[v].push_back(u);
}

This is going to give you problems!!!! It should not even compile!!!!!!!!!!!!!!!

adj[u] is an integer, not a vector. adj[u].push_back(v); makes no sense

---

Normally a adjacency matrix is used for this

Like so

void addEdge(
   std::vector<std::vector<<int>>& adj,
   int u, int v)
{
   adj[u].push_back(v);
   adj[v].push_back(u);
}

---

@aschepler points out you are using an unusual syntax to define your matrix. Please do not do this.

---

This is wrong

  for(int v = 0; v < V; ++v)
   {
      for(auto x: adj[v])
      {
         if(x == 0)
         {
            isolated++;
         }
      }
   }

Should be

  for(int v = 0; v < V; ++v)
   {
      if( ! adj[v].size() )
            isolated++;
   }