【高级技巧】拓扑排序：任务依赖的执行顺序求解封装

local deps = { B = { "A" }, C = { "A", "B" }, A = {} }
local function topoSort(deps)
    local indeg, out = {}, {}
    for task, pres in pairs(deps) do
        indeg[task] = indeg[task] or 0
        for _, p in ipairs(pres) do
            indeg[task] = indeg[task] + 1
        end
    end
    local queue = {}
    for t, d in pairs(indeg) do
        if d == 0 then
            queue[#queue + 1] = t
        end
    end
    while #queue > 0 do
        local t = table.remove(queue)
        out[#out + 1] = t
        for task, pres in pairs(deps) do
            for _, p in ipairs(pres) do
                if p == t then
                    indeg[task] = indeg[task] - 1
                    if indeg[task] == 0 then
                        queue[#queue + 1] = task
                    end
                end
            end
        end
    end
    return out
end
local order = topoSort(deps)
print(#order .. "/" .. 3)

local found = false
for _, t in ipairs(order) do
    if t == "C" then
        found = true
    end
end
print(found)