LeetCode Entry

2685. Count the Number of Complete Components

11.07.2026 medium 2026 kotlin rust

Fully connected components

2685. Count the Number of Complete Components medium substack youtube

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Problem TLDR

Fully connected components

Intuition

1. Union-Find to find connected components
2. Count incoming edges for each node
3. Fully connected group size is the number of edges for each node +1

Approach

• 50 elements can fit into long variable
• adjacency matrix would look the same for each group

Complexity

• Time complexity: \(O(n)\)

• Space complexity: \(O(n)\)

Code

    fun countCompleteComponents(n: Int, e: Array<IntArray>) = e
        .fold(LongArray(n){1L shl it}){ m, (a, b) -> m[a] += 1L shl b; m[b] += 1L shl a; m }
        .groupBy { it }.count { (k, v) -> v.size == k.countOneBits() }

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