October 4, 2021. A routine audit command goes wrong and Facebook withdraws the BGP routes to its own network. Every address it owns just stops existing as far as the rest of the internet is concerned, and it stays that way for six hours. The engineers who could undo it could not badge into the building, because the door system needed the network too. Answer the question the routers kept asking: is this address still announced?
Objective
Return whether an address is still covered by an announced block.
Steps
$ reachable({100,500}, {10,5}, 2, 105)
1
$ reachable({100,500}, {10,5}, 2, 110)
0
$ reachable({}, {}, 0, 100)
0
Expected files
Allowed functions
None. Write every helper yourself.
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