PhiPi from the Propeller forums pointed out that my simple id() function would treat the words “MOW” and “LOX” as the same. This means my code “accidently worked” for the dataset provided in the question.

PhiPi made a suggestion that I ran with. I tweaked the id() function and came up with this:


t = { "tsar", "rat", "tar", "star", "tars", "cheese", }
function id(s)
local t = {}
for i=1,26 do t[i] = 0 end
for i=1,#s do
local c = string.lower(s:sub(i,i))
if c >= "a" and c <= "z" then local h = string.byte(c) - ("a"):byte() + 1 if h > 0 then t[h] = t[h] + 1 end
end
end
local r = ""
for i=1,26 do
if t[i] > 0 then
r = r .. string.char(("a"):byte() + i - 1)
end
if t[i] > 1 then
r = r .. t[i]
end
end
return r
end
p = {} u = {}
print("* word -> id *")
for i=1,#t do
p[i] = 0
u[i] = id(t[i])
print(t[i], u[i])
end
for i=1,#u do
if p[i] == 0 then
p[i] = 1
print("===")
print(t[i])
for j=i+1,#u do
if p[j] == 0 and u[i] == u[j] then
p[j] = 1
print(t[j])
end
end
end
end


which outputs:


* word -> id *
tsar arst
rat art
tar art
star arst
tars arst
cheese ce3hs
===
tsar
star
tars
===
rat
tar
===
cheese


My friends on the Parallax Propeller forum posted the following quiz:

During a 45-minute Facebook job interview you could be requested to write a C++ from scratch that does this:
You have a list of these words
“tsar”, “rat”, “tar”, “star”, “tars”, “cheese”

re-arrange them so the anagrams (words that have the same letters) are grouped together.
output order not important.

Here’s my take (albeit in Lua instead of C++):

…and the output…

A Lua response to Problem 4:

Write a function that given a list of non negative integers, arranges them such that they form the largest possible number. For example, given [50, 2, 1, 9], the largest formed number is 95021.

function eval(a, i)
if not i then i = 1 max = 0 end
if i == #a then
local n = tonumber(table.concat(a))
if n > max then max = n end
else
for j=i,#a do
a[i],a[j] = a[j],a[i]
eval(a, i+1)
a[i],a[j] = a[j],a[i]
end
end
end
eval({50, 2, 1, 9})
io.write("max is ", max, "\n")
Output is:

max is 95021

A dude recently posted some programming challenges on his blog (here) that were mentioned on Reddit r/programming.

Problem 5 caught my eye and below, I’ve posted a short and sweet Lua brute-force to solve it:

Write a program that outputs all possibilities to put + or – or nothing between the numbers 1, 2, …, 9 (in this order) such that the result is always 100. For example: 1 + 2 + 34 – 5 + 67 – 8 + 9 = 100.

a = {
1, "", 2, "", 3, "", 4, "", 5, "",
6, "", 7, "", 8, "", 9
}
function inc(a)
for i=2,#a,2 do
if a[i] == "" then a[i] = "+" return true end
if a[i] == "+" then a[i] = "-" return true end
if a[i] == "-" then a[i] = "" end
end
return false
end
function eval(a)
local s = table.concat(a)
if loadstring("return " .. s)() == 100 then print(s) end
end
repeat eval(a) until inc(a) == false
Output looks like:

123-45-67+89
12-3-4+5-6+7+89
12+3+4+5-6-7+89
123+4-5+67-89
1+2+3-4+5+6+78+9
12+3-4+5+67+8+9
1+23-4+56+7+8+9
1+2+34-5+67-8+9
1+23-4+5+6+78-9
123+45-67+8-9
123-4-5-6-7+8-9


I bit the bullet and bought the “Engineer PA-09” crimping pliers for my board connectors. Just made a sample cable and I’m already pleased with the results. Totally worth the cost.

8-channel DAC and some connectors were added.

Opto isolator and 5-pin DIN connector.

Two rotary encoders and two potentiometers.

1st

2nd