#
# Program: Print numbers with a thousand separator as spaces in Ruby.
#
# Architecture notes:
# -------------------
# - Ruby does not provide built-in custom thousand separators.
# - We implement a manual formatter:
# * Convert the number to a string.
# * Handle negative numbers cleanly.
# * Insert spaces every three digits from the left.
# - The function is modular, reusable, and efficient.
#
# Performance notes:
# ------------------
# - O(n) time where n is the number of digits.
# - Memory usage is minimal; only small strings are created.
# - No external gems; uses only Ruby's standard library.
#
# Pitfalls:
# ---------
# - Must preserve the minus sign for negative numbers.
# - Must ensure correct grouping even for very large integers.
# - Avoid formatting floats unless converted to integers first.
#
# Security notes:
# ---------------
# - No external input parsing; safe for demonstration.
# - Avoid printing sensitive values in real systems.
#
# Tests:
# ------
# - Positive numbers
# - Negative numbers
# - Zero
# - Very large integers
#
# Format an integer using spaces as thousand separators.
def format_with_spaces(n)
s = n.to_s
# Handle negative numbers
is_negative = s.start_with?('-')
digits = is_negative ? s[1..] : s
len_digits = digits.length
# Determine how many digits before the first space
first_group = len_digits % 3
first_group = 3 if first_group == 0
result = ""
result << "-" if is_negative
# First group
result << digits[0, first_group]
# Remaining groups
pos = first_group
while pos < len_digits
result << " " << digits[pos, 3]
pos += 3
end
result
end
def main
tests = [
0,
42,
1234,
987_654_321,
-1_234_567,
1_000_000_000_000_000_000 # 10^18
]
puts "Running test cases:\n\n"
tests.each do |n|
puts "Original: #{n}"
puts "Formatted: #{format_with_spaces(n)}"
puts
end
end
main
# run:
#
# Running test cases:
#
# Running test cases:
#
# Original: 0
# Formatted: 0
#
# Original: 42
# Formatted: 42
#
# Original: 1234
# Formatted: 1 234
#
# Original: 987654321
# Formatted: 987 654 321
#
# Original: -1234567
# Formatted: -1 234 567
#
# Original: 1000000000000000000
# Formatted: 1 000 000 000 000 000 000
#
