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Maximum Flows on the Railway Network

Based on a 1940 Soviet railway network, find the maximum amount of cargo that can be transported from sources in the Western Soviet Union to destinations in Eastern European countries.

    
Wolfram Language code: railway = \!\(\*GraphicsBox[«6»]\);
The maximum flow value from indexed cities {1,5,6,7,9,12,13,18} to {44,40}:
Wolfram Language code: FindMaximumFlow[railway, {1, 5, 6, 7, 9, 12, 13, 18}, {44, 40}]
Visualize the flow:
Wolfram Language code: data = FindMaximumFlow[railway, {1, 5, 6, 7, 9, 12, 13, 18}, {44, 40}, "OptimumFlowData"];
Wolfram Language code: makelabels[railway_, data_] := Block[{edgecap = EdgeCapacity /. Options[railway, EdgeCapacity]}, Map[(# -> Framed[Style[Row[{edgecap[[EdgeIndex[railway, #]]] , "/", data[#]}], Directive[8.2, FontFamily -> "Helvetica"]], FrameMargins -> {{-.2, -.2}, {-.7, -.7}}, Background -> GrayLevel[.9], FrameStyle -> None])&, data["EdgeList"]] ];
Wolfram Language code: Annotate[data["FlowGraph"], {EdgeLabels -> makelabels[railway, data]}]