Lua线性建堆：自底向上的堆构造

local function build(t)
    for _, v in ipairs(t) do
        push(v)                     -- 逐个插入上浮n次
    end
end

local function sift(t, i, n)
    while true do
        local smallest, l, r = i, 2 * i, 2 * i + 1
        if l <= n and t[l] < t[smallest] then smallest = l end
        if r <= n and t[r] < t[smallest] then smallest = r end
        if smallest == i then break end
        t[i], t[smallest] = t[smallest], t[i]   -- 下沉交换
        i = smallest
    end
end
local function buildHeap(t)
    for i = math.floor(#t / 2), 1, -1 do
        sift(t, i, #t)              -- 倒序下沉建堆
    end
end