optimize allocations as MST has always n-1 connections where n is the number of nodes

Author: jbytecode

src/mst.jl

@@ -178,15 +178,19 @@ function solve(problem::MstProblem)::MstResult
 
     assigned = Set{Int64}()
     unassigned = nodes(conns)
-    connresult = Connection[]
+
+    n = length(unassigned)
+
+    # In MST, there must be n-1 connections for n nodes
+    connresult = Vector{Connection}(undef, n - 1)
 
     luckynode = pop!(unassigned)
     push!(assigned, luckynode)
 
-    while length(unassigned) > 0
+    for iter in 1:(n - 1)
         nearestnode, conn = findnearestbetweennodes(conns, distmat, assigned, unassigned)
         push!(assigned, nearestnode)
-        push!(connresult, conn)
+        connresult[iter] = conn
         totaldist += conn.value
         unassigned = filter(x -> x != nearestnode, unassigned)
     end

test/testmst.jl

@@ -88,6 +88,7 @@
         @test result isa MstResult
         @test result.distance == 30.0
         @test !hasloop(result.connections)
+        @test length(result.connections) == length(nodes(conns)) - 1
     end
 
     @testset "6 nodes with loops" begin
@@ -113,6 +114,7 @@
         end
 
         @test !hasloop(result.connections)
+        @test length(result.connections) == length(allnodes) - 1
     end
 
     @testset "7 nodes with loops" begin
@@ -149,6 +151,7 @@
         end
 
         @test !hasloop(result.connections)
+        @test length(result.connections) == length(allnodes) - 1
     end
 
     @testset "big network" begin
@@ -168,5 +171,6 @@
         end
 
         @test !hasloop(result.connections)
+        @test length(result.connections) == length(allnodes) - 1
     end
 end