Lua二叉树镜像：左右子树的递归互换

local function mirror(node)
    if node == nil then return end
    mirror(node.left)
    mirror(node.right)
    node.left, node.right = node.right, node.left
end

local function preorder(node, out)
    if node == nil then return end
    out[#out + 1] = node.val
    preorder(node.left, out)
    preorder(node.right, out)
end
local root = {val = 1, left = {val = 2, left = {val = 4}},
    right = {val = 3}}
mirror(root)
local out = {}
preorder(root, out)
local p = getplayerbyname("mirror01")
sendmsg(p, 1, table.concat(out, ","))