How to randomly pick a vertices from graph? - c++

Question

I am looking for solution to pick a number randomly from graph using c++.
For example I have a graph that add edge (one or more) between two vertices, how can I pick a number randomly?
some of code :
#include <iostream>
#include <list>
#include <queue>
using namespace std;
// Graph class represents a undirected graph using adjacency list representation
class Graph
{
private:
int V; // # of vertices
list<int> *adj; // Pointer to an array containing adjacency lists
public:
Graph(int V) // Constructor
{
this->V = V;
adj = new list<int>[V];
}
void addEdge(int v, int w); // function to add an edge to graph
void print(int v, int w); //function to display
};
void Graph::addEdge(int v, int w)
{
adj[v].push_front(w); // Add w to v’s list.
adj[w].push_front(v); // Add v to w’s list.
print(v, w);
}
void Graph::print(int v, int w) {
cout << v << " - " << w << endl;}
In the main:
Graph g(4);
g.addEdge(0, 1);
g.addEdge(0, 2);
g.addEdge(1, 3);
Sample output:
0 - 1 0 - 2 1 - 3

Answer 1

Use math lib. Rand function. Select random num and select (0 to number of edges-1) from list of edges, then select another random number and select that vertex of the edge, 0 or 1 (bottom/top vertex of edge)

Answer 2

#include <stdlib.h>
#include <iostream>
#include <list>
#include <queue>
using namespace std;
// Graph class represents a undirected graph using adjacency list representation
class Graph
{
private:
int V; // # of vertices
list<int> *adj; // Pointer to an array containing adjacency lists
public:
Graph(int V) // Constructor
{
this->V = V;
adj = new list<int>[V];
}
void addEdge(int v, int w); // function to add an edge to graph
void print(int v, int w); //function to display
};
void Graph::addEdge(int v, int w)
{
adj[v].push_front(w); // Add w to v’s list.
adj[w].push_front(v); // Add v to w’s list.
print(v, w);
}
int Graph::getRandomVertexFromEdge()
{
int list_size_divided_by_2 = adj.size() / 2;
int rEdge = (rand() % list_size_divided_by_2);
int rVW = (rand() % 1);
int ret = adj[(rEdge + rVW)];
//this will return a random vertex from a random edge;
print(rEdge,rVW);
return ret;
}
void Graph::print(int v, int w) {
cout << v << " - " << w << endl;}