【高级技巧】最小生成树：地图路网的最低成本连接

local function prim(nodes, dist)
    local n = #nodes
    local inTree = { [1] = true }
    local total, edges = 0, {}
    for _ = 2, n do
        local bestLen, bestA, bestB = math.huge
        for a in pairs(inTree) do
            for b = 1, n do
                if not inTree[b] and dist[a][b] < bestLen then
                    bestLen, bestA, bestB = dist[a][b], a, b
                end
            end
        end
        inTree[bestB] = true
        total = total + bestLen
        edges[#edges + 1] = bestA .. "-" .. bestB
    end
    return total, edges
end

local nodes = { "比奇", "沃玛森林", "白日门" }
local dist = {
    [1] = { [2] = 30, [3] = 90 },
    [2] = { [3] = 40 }
}
dist[2][1], dist[3][1], dist[3][2] = 30, 90, 40
local total, edges = prim(nodes, dist)
print(total, table.concat(edges, ","))