-- The Computer Language Benchmarks Game
-- http://shootout.alioth.debian.org/
-- contributed by Mike Pall

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

local function ItemCheck(tree)
  if tree[2] then
    return tree[1] + ItemCheck(tree[2]) - ItemCheck(tree[3])
  else
    return tree[1]
  end
end

local N = 12
local mindepth = 4
local maxdepth = mindepth + 2
if maxdepth < N then maxdepth = N end

local start = os.clock()

do
  local stretchdepth = maxdepth + 1
  local stretchtree = BottomUpTree(0, stretchdepth)
  io.write(string.format("stretch tree of depth %d check: %d\n",
    stretchdepth, ItemCheck(stretchtree)))
end

local longlivedtree = BottomUpTree(0, 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(1, depth)) +
            ItemCheck(BottomUpTree(-1, depth))
  end
  io.write(string.format("%d trees of depth %d check: %d\n",
    iterations*2, depth, check))
end

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

io.write(string.format("elapsed: %.8f\n", os.clock() - start))