unique_letters.rb

# Implement an algorithm 
# to determine if a string has all unique characters 
# without using uniq. 
# What if you can not use additional data structures?

# ===

sample = "abcdę"
sample.split('').uniq.count == sample.split('').count
sample.split('').uniq.count == sample.length
sample.split('').uniq.join == sample

# Without uniq:

letters = sample.split('')
result = true
unique_letters = []
letters.each do |letter|
  if unique_letters.include?(letter)
    result = false
    break
  else
    unique_letters << letter
  end
end
result

# In English

# 1. Cut the string into a collection of letters
# 2. Start with an empty array
# 3. Go through the collection of letters and...
#    A. If the letter is not in the array from (2), add it
#    B. If the letter is in the array from (2), do nothing
# 4. Merge the letters in the array from (2) back into a single string
# 5. The letters are all unique if the string from (4) is equal to the original string

# 1. From 0 to the length of the string as "i"...
# 2. Find the count of the letter at position "i"
#   3. Add that count to a total
#   4. If total is equal to the length of the string then the letters are unique_letters

#   3. If the count is >1 then fail
#   4. Otherwise pass

sample = "abcd"
result = true
(0...sample.length).each do |i|
  if sample.count( sample[i] ) > 1
    result = false
  end
end