#! /usr/bin/lua

-- by Michael Anderson at
-- https://stackoverflow.com/questions/8722620/comparing-two-index-tables-by-index-value-in-lua
-- modified by Roger
function recursive_compare(t1,t2)
  -- Use usual comparison first.
  if t1==t2 then return true end
  -- We only support non-default behavior for tables
  if (type(t1)~="table") then return false end
  -- They better have the same metatables
  local mt1 = getmetatable(t1)
  local mt2 = getmetatable(t2)
  if( not recursive_compare(mt1,mt2) ) then return false end
  -- Build list of all keys
  local kk = {}
  for k1, _ in pairs(t1) do
     kk[k1] = true
  end
  for k2, _ in pairs(t2) do
     kk[k2] = true
  end
  -- Check each key that exists in at least one table
  for _, k in ipairs(kk) do
     if (not recursive_compare(t1[k], t2[k])) then
        return false
     end
  end
  return true
end

function shortestdistance(a0)
   if #a0 % 2 ~= 0 then
      return {}
   end
   local a = a0
   table.sort(a)
   local out = {}
   for i = 1, #a, 2 do
      if a[i] ~= a[i+1] then
         return {}
      end
      table.insert(out, {a[i], a[i]})
   end
   return out
end

if recursive_compare(shortestdistance({3, 2, 3, 2, 2, 2}), {{2, 2}, {2, 2}, {3, 3}}) then
  io.write("Pass")
else
  io.write("FAIL")
end
io.write(" ")

if recursive_compare(shortestdistance({1, 2, 3, 4}), {}) then
  io.write("Pass")
else
  io.write("FAIL")
end
print("")