【数据结构】图的广度优先搜索

#include<list>
#include<iostream>
//Program to print BFS traversal from a given source vertex. BFS(int s)
//traverses vertices reachable from s 
using namespace std;

//The class represents  a directed graph using adjacency lists
class Graph {
    int V;    //No. of vertices
    list<int> *adj;
 public:
     Graph(int V);    //Constructor
     ~Graph();　　//Destructor
     void addEdge(int v, int w);    //function to add an edge to graph
     void BFS(int s);    //print BFS traversal from a given source s
};

Graph::Graph(int V) {
    this->V = V;
    adj = new list<int>[V];
}

Graph::~Graph() {
    delete []adj;
}

void Graph::addEdge(int v, int w) {
    adj[v].push_back(w);
}

void Graph::BFS(int s) {
    //Mark all the vertices as not visited
    bool *visited = new bool[V];
    for (int i = 0; i < V; i++) {
        visited[i] = false;
    }

    //Create a queue for BFS
    list<int> queue;

    //Mark the current node as visited and enqueue it 
    visited[s] = true;
    queue.push_back(s);

    //"i" will be used to get all adjacent vertices of vertex
    list<int>::iterator i;

    while (!queue.empty()) {
        //Dequeue a vertex from queue and print it
        s = queue.front();
        cout<<s<<" ";
        queue.pop_front();

        //Get all adjacent vertices of the Dequeued vertex s
        //If a adjacent has not been visited, then mark it visited 
        //and enqueue it
        for (i = adj[s].begin(); i != adj[s].end(); i++) {
            if (!visited[*i]) {
                visited[*i] = true;
                queue.push_back(*i);
            }
        }
    }

    delete []visited;
}

int main()
{
     // Create a graph given in the above diagram
    Graph g(4);
    g.addEdge(0, 1);
    g.addEdge(0, 2);
    g.addEdge(1, 2);
    g.addEdge(2, 0);
    g.addEdge(2, 3);
    g.addEdge(3, 3);
 
    cout << "Following is Breadth First Traversal (starting from vertex 2) \n";
    g.BFS(2);
 
    return 0;
}