reorg and add code for second edition

09_dijkstras_algorithm/julia/01_dijkstras_algorithm.jl

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+# Julia version: LTS (v1.0.3)
+using Test
+
+graph = Dict()
+graph["start"] = Dict()
+graph["start"]["a"] = 6
+graph["start"]["b"] = 2
+
+graph["a"] = Dict()
+graph["a"]["fin"] = 1
+
+graph["b"] = Dict()
+graph["b"]["a"] = 3
+graph["b"]["fin"] = 5
+
+graph["fin"] = Dict()
+
+# the costs table
+infinity = Inf
+costs = Dict()
+costs["a"] = 6
+costs["b"] = 2
+costs["fin"] = infinity
+
+# the parents table
+parents = Dict()
+parents["a"] = "start"
+parents["b"] = "start"
+parents["fin"] = nothing
+
+processed = []
+
+function find_lowest_cost_node(costs)
+    lowest_cost = Inf
+    lowest_cost_node = nothing
+    for node in keys(costs)
+        cost = costs[node]
+        if cost < lowest_cost && node ∉ processed
+            lowest_cost = cost
+            lowest_cost_node = node
+        end
+    end
+    return lowest_cost_node
+end
+
+node = find_lowest_cost_node(costs)
+while node != nothing
+    global node
+    cost = costs[node]
+    neighbors = graph[node]
+    for n in keys(neighbors)
+        new_cost = cost + neighbors[n]
+        if costs[n] > new_cost
+            costs[n] = new_cost
+            parents[n] = node
+        end
+    end
+    push!(processed,node)
+    node = find_lowest_cost_node(costs)
+end
+
+println("Cost from the start to each node:")
+println(costs)
+@test costs == Dict("fin"=>6,"b"=>2,"a"=>5)