Critical Connections (Bridges)

n servers (0 to n - 1) are joined by undirected connections. The network is connected. A connection is critical (a bridge) if removing it makes some servers unable to reach each other. Return all critical connections as [a, b] with a < b, sorted.

For n = 4 and connections = [[0, 1], [1, 2], [2, 0], [1, 3]] the answer is [[1, 3]].

Examples

Example 1

Input:

critical_connections(4, [[0, 1], [1, 2], [2, 0], [1, 3]])

Output:

[[1, 3]]

Example 2

Input:

critical_connections(2, [[0, 1]])

Output:

[[0, 1]]

Constraints

• 2 <= n <= 100000
• n - 1 <= len(connections) <= 200000
• No repeated connections, no self-loops.