Add & Remove Edges - Educational Content

Modifying graph structure using a set-based adjacency list.

Using Python's set for neighbor lists makes adding and removing edges highly efficient, typically an O(1) operation on average.
To maintain the graph's integrity, it's crucial to perform the operation in both directions. Forgetting `adj[v].add(u)` after `adj[u].add(v)` would break the symmetry of an undirected graph.
The `.discard()` method is used for removal because it won't raise an error if the edge doesn't exist, making the function more robust.

Python: Undirected Edge Modification

def add_edge(adj,u,v):
    adj[u].add(v); adj[v].add(u)
def remove_edge(adj,u,v):
    adj[u].discard(v); adj[v].discard(u)