Implement is_articulation to check if vertex is articulation point
#387
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Timing-wise, julia> g = path_graph(5)
julia> articulation(g) # [2, 3, 4]
julia> @btime 2 ∈ articulation($g) # 209.656 ns (8 allocations: 704 bytes)
julia> @btime is_articulation($g, 2) # 122.850 ns (4 allocations: 464 bytes)
julia> g = path_graph(15)
julia> articulation(g) # [2:14...]
julia> @btime 9 ∈ articulation($g) # 453.853 ns (10 allocations: 2.16 KiB)
julia> @btime is_articulation($g, 9) # 245.286 ns (4 allocations: 624 bytes) |
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## master #387 +/- ##
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- Coverage 97.31% 97.30% -0.02%
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Files 120 120
Lines 6954 6965 +11
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+ Hits 6767 6777 +10
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Bump. |
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Bump :) |
| @@ -1,6 +1,6 @@ | |||
| name = "Graphs" | |||
| uuid = "86223c79-3864-5bf0-83f7-82e725a168b6" | |||
| version = "1.11.1" | |||
| version = "1.11.2" | |||
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merge default branch into this PR, the version has evolved since
| s = Vector{Tuple{T,T,T}}() | ||
| low = zeros(T, nv(g)) | ||
| pre = zeros(T, nv(g)) |
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If the idea is to call is_articulation several times in a row for different vertices, these allocations might be reusable? Maybe we should expose articulation_dfs!?
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Sure, that'd be alright with me also. The _dfs part is an implementation detail though, so maybe this should just be called is_articulation!, taking work-arrays for pre and low then? Let me know what you think and I'll change to that.
| s::Vector{Tuple{T,T,T}}, | ||
| low::Vector{T}, | ||
| pre::Vector{T}, |
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I admit, I don't recall: this was mainly a refactoring of the original code and I just kept the variable names as they were.
| if !isnothing(is_articulation_pt) | ||
| if pre[u] != 0 | ||
| return is_articulation_pt | ||
| end | ||
| end |
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Can you explain this shortcut in a comment?
Co-authored-by: Guillaume Dalle <[email protected]>
This factors out the DFS step from
articulationinto a separate functionarticulation_dfs!and then uses this new function to implementis_articulation(g, v)which checks whethervis an articulation point ofgwithout necessarily computing all the articulation points.The branching on
isnothing(is_articulation_pts)inarticulation_dfs!is a bit inelegant - as is the fact thatarticulation_dfs!doesn't mutate ifis_articulation_pts === nothing, but it seemed the simplest way to avoid code duplication.Aside from these additions, I revised the doc string of
articulation(g)a bit (e.g., it 1. previously misleadingly stated thatghad to be connected; it does not; and 2. it changed nomenclature from "articulation point" to "cut vertex" mid-sentence).