Step 2: Adding Friendships (`add`)

When we `add u v`, we must update our adjacency list. Since friendships are mutual (undirected), we must update two lists.

Guidance for Step 2

  • Mutual Friendship: If `u` is friends with `v`, then `v` is friends with `u`. You must add `v` to `adj[u]` AND add `u` to `adj[v]`.
  • Avoid Duplicates: To prevent `[1, 1]` in a friend list, check if a friendship already exists before adding it.
  • Your Task: Fill in the blanks to correctly add a friendship. 
...
    if op == "add":
        u, v = int(parts[1]), int(parts[2])

        # --- BLANK 1 ---
        # We only add the friendship if they aren't already friends.
        if _____________________:
        
            # --- BLANK 2 ---
            # Undirected graph: add edge in both directions
            _________________
            _________________

    elif op == "degree":
...
Copied!