binary_trees.lua

-- The Computer Language Benchmarks Game
-- http://benchmarksgame.alioth.debian.org/
-- 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 6
local mindepth = 4
local maxdepth = mindepth + 2
if maxdepth < N then maxdepth = N end

do
  local stretchdepth = maxdepth + 1
  local stretchtree = BottomUpTree(stretchdepth)
  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
  string.format("%d\t trees of depth %d\t check: %d\n",
    iterations, depth, check)
end

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