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

local function fannkuch(n: integer)
  local p: integer[], q :integer[],
        s: integer[], sign: integer,
	maxflips: integer,
	sum: integer = {}, {}, {}, 1, 0, 0
  for i=1,n do 
    p[i] = i 
    q[i] = i
    s[i] = i 
  end
  repeat
    -- Copy and flip.
    local q1: integer = p[1]  -- Cache 1st element.
    if q1 ~= 1 then
      for i=2,n do 
        q[i] = p[i] 
      end                     -- Work on a copy.
      local flips: integer = 1
      repeat
        local qq: integer = q[q1]
        if qq == 1 then	      -- ... until 1st element is 1.
          sum = sum + sign*flips
          if flips > maxflips then 
            maxflips = flips 
          end -- New maximum?
	  break
        end
        q[q1] = q1
        if q1 >= 4 then
          local i: integer, j: integer = 2, q1 - 1
          repeat 
            q[i], q[j] = q[j], q[i]; 
            i = i + 1; 
            j = j - 1; 
          until i >= j
        end
        q1 = qq;
        flips = flips + 1
      until false
    end
    -- Permute.
    if sign == 1 then
      p[2], p[1] = p[1], p[2]; sign = -1	-- Rotate 1<-2.
    else
      p[2], p[3] = p[3], p[2]; sign = 1		-- Rotate 1<-2 and 1<-2<-3.
      for i=3,n do
        local sx: integer = s[i]
        if sx ~= 1 then 
          s[i] = sx-1; 
          break 
        end
        if i == n then 
          return sum, maxflips 
        end	-- Out of permutations.
	s[i] = i
	-- Rotate 1<-...<-i+1.
	local t: integer = p[1]; 
        for j=1,i do 
          p[j] = p[j+1] 
        end; 
        p[i+1] = t
      end
    end
  until false
end

local n = tonumber(arg and arg[1]) or 11
ravi.compile(fannkuch, {omitArrayGetRangeCheck=1})
local t1 = os.clock()
local sum, flips = fannkuch(n)
local t2 = os.clock()
io.write(sum, "\nPfannkuchen(", n, ") = ", flips, "\n")
io.write("elapsed time in secs ", (t2-t1), "\n")

--ravi.dumplua(fannkuch)
