Lua二叉树中序遍历：左根右的访问次序

visit(node)              -- 先访问根，顺序打乱
walk(node.left)
walk(node.right)

local function inorder(node, out)
    if node == nil then return end
    inorder(node.left, out)
    table.insert(out, node.val)
    inorder(node.right, out)
end
local root = {val = 50,
    left = {val = 30, left = {val = 20}, right = {val = 40}},
    right = {val = 70, left = {val = 60}, right = {val = 80}}}
local out = {}
inorder(root, out)
local p = getplayerbyname("sort02")
sendmsg(p, 1, table.concat(out, ","))
-- 输出 20,30,40,50,60,70,80