Graph implementation using STL for competitive programming | Set 1 (DFS of Unweighted and Undirected)

We have introduced Graph basics in Graph and its representations. In this post, a different STL based representation is used that can be helpful to quickly implement graph using vectors. The implementation is for adjacency list representation of graph.

Following is an example undirected and unweighted graph with 5 vertices.

Below is adjacency list representation of the graph.

We use vector in STL to implement graph using adjacency list representation.

The idea is to represent graph as an array of vectors such that every vector represents adjacency list of a vertex. Below is complete STL based C++ program for DFS Traversal.





// A simple representation of graph using STL,
// for the purpose of competitive programming
using namespace std;
// A utility function to add an edge in an
// undirected graph.
void addEdge(vector<int> adj[], int u, int v)
// A utility function to do DFS of graph
// recursively from a given vertex u.
void DFSUtil(int u, vector<int> adj[],
                    vector<bool> &visited)
    visited[u] = true;
    cout << u << " ";
    for (int i=0; i<adj[u].size(); i++)
        if (visited[adj[u][i]] == false)
            DFSUtil(adj[u][i], adj, visited);
// This function does DFSUtil() for all 
// unvisited vertices.
void DFS(vector<int> adj[], int V)
    vector<bool> visited(V, false);
    for (int u=0; u<V; u++)
        if (visited[u] == false)
            DFSUtil(u, adj, visited);
// Driver code
int main()
    int V = 5;
    // The below line may not work on all
    // compilers.  If it does not work on
    // your compiler, please replace it with
    // following
    // vector<int> *adj = new vector<int>[V];
    vector<int> adj[V];
    // Vertex numbers should be from 0 to 4.
    addEdge(adj, 0, 1);
    addEdge(adj, 0, 4);
    addEdge(adj, 1, 2);
    addEdge(adj, 1, 3);
    addEdge(adj, 1, 4);
    addEdge(adj, 2, 3);
    addEdge(adj, 3, 4);
    DFS(adj, V);
    return 0;

Output :

0 1 2 3 4

Below are related articles:
Graph implementation using STL for competitive programming | Set 2 (Weighted graph)
Dijkstra’s Shortest Path Algorithm using priority_queue of STL
Dijkstra’s shortest path algorithm using set in STL
Kruskal’s Minimum Spanning Tree using STL in C++
Prim’s algorithm using priority_queue in STL

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Improved By : Akanksha_Rai

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