Don't use pushfirst!

Author: amontoison

src/order.jl

@@ -343,17 +343,19 @@ function vertices(
     db = DegreeBuckets(
         T, degrees, max_degrees; reproduce_colpack=order.reproduce_colpack
     )
-    π = T[]
-    sizehint!(π, nb_vertices(g))
-    for _ in 1:nb_vertices(g)
+    π = Vector{T}(undef, nb_vertices(g))
+    for index in 1:nb_vertices(g)
         u = pop_next_candidate!(db; direction)
-        direction == :low2high ? push!(π, u) : pushfirst!(π, u)
+        π[index] = u
         for v in neighbors(g, u)
             !has_diagonal(g) || (u == v && continue)
             already_ordered(db, v) && continue
             update_bucket!(db, v; degtype, direction)
         end
     end
+    if direction == :low2high
+        reverse!(π)
+    end
     return π
 end
 
@@ -389,11 +391,10 @@ function vertices(
         fill!(degrees, zero(T))
     end
     db = DegreeBuckets(T, degrees, maxd2; reproduce_colpack=order.reproduce_colpack)
-    π = T[]
-    sizehint!(π, n)
-    for _ in 1:nb_vertices(g, Val(side))
+    π = Vector{T}(undef, n)
+    for index in 1:nb_vertices(g, Val(side))
         u = pop_next_candidate!(db; direction)
-        direction == :low2high ? push!(π, u) : pushfirst!(π, u)
+        π[index] = u
         for w in neighbors(g, Val(side), u)
             for v in neighbors(g, Val(other_side), w)
                 if v != u && !visited[v]
@@ -411,6 +412,9 @@ function vertices(
         end
         num_visited = 0
     end
+    if direction == :low2high
+        reverse!(π)
+    end
     return π
 end