cocktail sort

Data

in lua

Tags

exchange sort, sorting

Source Code

``````-- (Optimized) Cocktail sort implementation
-- See: http://en.wikipedia.org/wiki/Cocktail_sort

-- list: a list to be sorted (in-place)
-- comp : (Optional) a comparison function
--  defaults to function(a,b) return a < b end
return function (list, comp)
comp = comp or function(a,b) return a < b end
local begin, _end = 0, #list - 1

repeat
local swapped = false
begin = begin + 1
for i = begin, _end do
if not comp(list[i], list[i+1]) then
list[i], list[i+1] = list[i+1], list[i]
swapped = true
end
end
if not swapped then break end
_end = _end - 1
for i = _end, begin, -1 do
if not comp(list[i], list[i+1]) then
list[i], list[i+1] = list[i+1], list[i]
swapped = true
end
end
until not swapped
return list
end

``````
``````-- Tests for cocktail_sort.lua
local cocktail_sort = require 'cocktail_sort'

local total, pass = 0, 0

local function dec(str, len)
return #str < len
and str .. (('.'):rep(len-#str))
or str:sub(1,len)
end

local function run(message, f)
total = total + 1
local ok, err = pcall(f)
if ok then pass = pass + 1 end
local status = ok and 'PASSED' or 'FAILED'
print(('%02d. %68s: %s'):format(total, dec(message,68), status))
end

-- Wrap for Lua's table sort so that it returns
-- the passed-in table
local function sort(t, comp)
table.sort(t, comp)
return t
end

-- Returns a copy of a an array
local function clone(t)
local _t = {}
for k,v in ipairs(t) do _t[k] = v end
return _t
end

-- Checks if t1 and t2 arrays are the same
local function same(t1, t2)
for k,v in ipairs(t1) do
if t2[k] ~= v then return false end
end
return true
end

-- Generates an array of n values in random order
local function gen(n)
local t = {}
for i = 1, n do t[i] = math.random(n) end
return t
end

-- Note: Let's add a bit of randomness
math.randomseed(os.time())

run('Empty arrays', function()
local t = {}
assert(same(sort(clone(t)),cocktail_sort(t)))
end)

run('Sorted array', function()
local t = {1, 2, 3, 4, 5}
assert(same(sort(clone(t)),cocktail_sort(t)))
end)

run('Array sorted in reverse', function()
local t = {5, 4, 3, 2, 1}
assert(same(sort(clone(t)),cocktail_sort(t)))
local t = {5, 4, 3, 2, 1}
local comp = function(a,b) return a>b end
assert(same(sort(clone(t), comp),cocktail_sort(t, comp)))
end)

run('Array containing multiple occurences of the same value', function()
local t = {4, 4, 8, 2, 2}
local comp = function(a,b) return a <= b end
assert(same(sort(clone(t)),cocktail_sort(t, comp)))
local t = {0, 0, 0, 0, 0}
local comp = function(a,b) return a <= b end
assert(same(sort(clone(t)),cocktail_sort(t, comp)))
end)

run('Large array of random values (1e3 values)', function()
local t = gen(1e3)
local comp = function(a,b) return a <= b end
assert(same(sort(clone(t)),cocktail_sort(t, comp)))
end)

print(('-'):rep(80))
print(('Total : %02d: Pass: %02d - Failed : %02d - Success: %.2f %%')
:format(total, pass, total-pass, (pass*100/total)))``````