Graph Representation: Adjacency List

We don't get 'Node' objects automatically. Often, inputs are given as a list of Edges or integer pairs.

Input: n = 4, edges = [[0,1], [0,2], [2,3]].

We need to convert this into a structure that allows fast lookups of neighbors: getNeighbors(u).

Adjacency Matrix: A 2D array adj[n][n] where adj[i][j] = 1 if connected.

• Pros: O(1) edge check.
• Cons: O(N²) space. Slow to iterate neighbors O(N).

Adjacency List: A Map or Array of Lists where adj[i] contains a list of neighbors.

• Pros: O(V + E) space. Fast to iterate neighbors.
• Verdict: Almost always use Adjacency List for interview problems unless N is very small or the graph is dense.

Visualizing Graph Edges.