【高级技巧】环形单链表：循环队列的链表实现封装

local function newNode(val)
    return { val = val, next = nil }
end
local function newRing()
    local head = newNode(nil)
    head.next = head
    return { head = head, size = 0 }
end
local function pushBack(ring, val)
    local node = newNode(val)
    node.next = ring.head
    local cur = ring.head
    while cur.next ~= ring.head do
        cur = cur.next
    end
    cur.next = node
    ring.size = ring.size + 1
end
local function popFront(ring)
    if ring.size == 0 then
        return nil
    end
    local head = ring.head
    local val = head.next.val
    head.next = head.next.next
    ring.size = ring.size - 1
    return val
end

local queue = newRing()
pushBack(queue, "任务甲")
pushBack(queue, "任务乙")
print(popFront(queue))