binary-trees Lua #2 program

-- The Computer Language Benchmarks Game
-- https://salsa.debian.org/benchmarksgame-team/benchmarksgame/
-- contributed by Mike Pall
-- *reset*

local function BottomUpTree(depth)
  if depth > 0 then
    depth = depth - 1
    local left, right = BottomUpTree(depth), BottomUpTree(depth)
    return { left, right }
  else
    return { }
  end
end

local function ItemCheck(tree)
  if tree[1] then
    return 1 + ItemCheck(tree[1]) + ItemCheck(tree[2])
  else
    return 1
  end
end

local N = tonumber(arg and arg[1]) or 0
local mindepth = 4
local maxdepth = mindepth + 2
if maxdepth < N then maxdepth = N end

do
  local stretchdepth = maxdepth + 1
  local stretchtree = BottomUpTree(stretchdepth)
  io.write(string.format("stretch tree of depth %d\t check: %d\n",
    stretchdepth, ItemCheck(stretchtree)))
end

local longlivedtree = BottomUpTree(maxdepth)

for depth=mindepth,maxdepth,2 do
  local iterations = 2 ^ (maxdepth - depth + mindepth)
  local check = 0
  for i=1,iterations do
    check = check + ItemCheck(BottomUpTree(depth))
  end
  io.write(string.format("%d\t trees of depth %d\t check: %d\n",
    iterations, depth, check))
end

io.write(string.format("long lived tree of depth %d\t check: %d\n",
  maxdepth, ItemCheck(longlivedtree)))
    

NOTES:
64-bit Ubuntu quad core
Lua 5.4.0  Copyright (C) 1994-2020 Lua.org, PUC-Rio


Tue, 30 Jun 2020 22:40:56 GMT

COMMAND LINE:
/opt/src/lua-5.4.0/bin/lua  binarytrees.lua-2.lua 21

PROGRAM OUTPUT:
stretch tree of depth 22	 check: 8388607
2097152	 trees of depth 4	 check: 65011712
524288	 trees of depth 6	 check: 66584576
131072	 trees of depth 8	 check: 66977792
32768	 trees of depth 10	 check: 67076096
8192	 trees of depth 12	 check: 67100672
2048	 trees of depth 14	 check: 67106816
512	 trees of depth 16	 check: 67108352
128	 trees of depth 18	 check: 67108736
32	 trees of depth 20	 check: 67108832
long lived tree of depth 21	 check: 4194303