Introduction to Graphs Representation and Implementation

Graphs can be represented in two forms in code:

1. Adjacency List: Let adj be a list of vectors of size n then adj[u] will be a list that contains v
2. Adjacency Matrix: Let adj be a matrix of size nxn and for each edge (u,v) in the matrix: adj[u][v] = 1

Adjacency List

vector<vector<int>> adj (n);
// for each edge u,v: v should be an element of adj[u] (and vice versa for undirected graphs)
 
for (int i = 0; i < edgeCount; i++) {
	int u, v;
	cin >> u >> v;
	adj[u].push_back(v);
	
}

Adjacency Graph.

array<array<int,n>,n> adj;
// for each edge u,v: v should be an element of adj[u] (and vice versa for undirected graphs)
 
for (int i = 0; i < edgeCount; i++) {
	int u, v;
	cin >> u >> v;
	adj[u][v] = 1;
}