Union Find (Disjoint Set) - when to use it over BFS/DFS

Union Find confused me for a long time because BFS/DFS can solve most connectivity problems. Here's when Union Find is better:

Use Union Find when:

• You need to check connectivity repeatedly (amortized O(α(n)) per query)
• Elements are added incrementally
• You need to merge groups dynamically

Use BFS/DFS when:

• You need shortest path
• You need to traverse in a specific order
• It's a one-time query

Classic Union Find problems:

• Number of connected components
• Redundant connection
• Accounts merge
• Earliest moment when everyone becomes friends

With path compression + union by rank, it's almost O(1) per operation. Beautiful data structure.