Weekend Ruby practice

ruby_practice.rb

def fibonacci(n)
  if (0..1) === n
    n
  else
    fibonacci(n-1) + fibonacci(n-2)
  end
end

def prime_list(highest)
  list = Array.new(highest, true)
  # Because 0 and 1 are not primes, and we want the indices to match.
  list[0..1] = false, false
  # If a number has a factor greater than its square root, then it also has a factor less than its square root.
  limit = Math.sqrt(highest)
  test = 2

  while test < limit
    multiple = 2*test

    while multiple < highest
      list[multiple] = false
      multiple += test
    end

    # Find the first instance of true after test. This is our next highest prime.
    test = list[(test+1)..highest].index(true) + test + 1
  end

  # Use this line without what's below to get the last prime.
  # list.rindex(true)

  list.each_with_index do |bool, index| 
    if bool
      list[index] = index
    end
  end

  list.select { |entry| entry }

end

def pair_array_to_hash(pair_array)
  hash = Hash.new
  pair_array.each do |pair|
    hash[pair[0]] = pair[1]
  end
  hash
end

def string_compressor(string)
  output_string = ''
  char = 1
  counter = 1

  while char <= string.length
    if string[char] == string[char-1]
      counter += 1
    else
      unless counter == 1; output_string << counter.to_s end
      output_string << string[char-1]
      counter = 1
    end
    char += 1
  end

  output_string
end

def multiplication_table(n, m)
  cell_size = (n*m).to_s.length + 1

  (1..n).map do |row_num|
    row = (1..m).map do |col_num|
      number = (col_num*row_num).to_s
      ' '*(cell_size - number.length) + number
    end
    puts row.join('')
  end

end

def pascal_triangle(rows)
  row_array = Array.new(rows+1) {Hash.new(0)}
  row_array[0][0] = 1

  (1..rows).each do |size|
    (0..size).each do |entry|
      row_array[size][entry] = row_array[size-1][entry-1] + row_array[size-1][entry]
    end
  end

  # Now convert to strings
  biggest = row_array.last.length/2
  cell_width = row_array.last[biggest].to_s.length * 2

  row_array.map! do |row|
    row.each_pair do |key, value|
      row[key] = ' '*(cell_width - value.to_s.length) + value.to_s
    end
    row[0] = row[0].lstrip
    row = row.values.join('')
  end

  row_width = row_array.last.length
  row_array.each do |row|
    puts row.center(row_width)
  end

end