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# Soros Tutorial Four 👪 Reference & Group
#
# We will write a thousand separation program
# by referring parts of the input text and
# learning more about regular expression syntax.
#
#
#
# TASK 1
#
# We can create character groups in the regex pattern by
# parenthesizing, and refer them using reference \1..\9
# in the regex replacement.
#
# For example, following program replaces the
# characters of arbitry 2-character input (ab -> ba, etc.):
#
# (.)(.) \2\1
#
# Write a program to return with the last two characters of the
# input!
# TASK 2
#
# Character sequences in bracket expression can be abbreviated
# using character ranges separated by a hyphen character.
#
# For example, [a-z] matches every character between “a” and “z”,
# [a-cx-z] matches letter a, b, c, x, y and z.
#
# Using this write a program to return with the first character
# of the input, if that is between 1 and 5, or 9!
# TASK 3
#
# Bracket expression [^...] matches complementers of the
# given characters or character ranges. For example,
# [^01] matches every character, except 0 or 1.
#
# Write a program to return with the last two characters
# of the input, if they don’t contain zeroes.
# TASK 4
#
# The pattern \d matches an arbitrary digit. For example
# \d\d\d matches every 3-digit numbers.
#
# Using this, write a program to return with the first
# three digits of the input!
# TASK 5
#
# Repetition sign + and * can be combined with bracket
# expressions, \d and groups, too. There are three other
# frequently used repetitions:
#
# ? 0, or 1 times
# {n} exactly n times
# {n,m} between n and m times
#
# For example, \d{6}, \d{1,3}
#
# Using this, write a program to do thousand separation
# between 1 and 100,000,000,000.
#
# Rules:
#
# I. Separation is only from 5-digit numbers.
# For example: 1, 10, 1000, 10,000.
#
# II. Separate by commas by 3-digit groups from the right side
# For example: 100,000, 1000,000, 10,000,000, 100,000,000...
#
# NOTE: Test your program by typing a single number in the textbox “Input”.
# OPTIONAL TASK 1
#
# Groups can match different patterns:
#
# (word1|word2|word3)
#
# matches word1 OR word2 OR word3.
#
# For example, ([a-z]|10*) matches a single letter OR
# 10 OR 100 OR 1000 etc.
#
# Groups can contain inner groups, too.
#
# Guess it, what does the following expression!
#
# ((Anne|Becky) (Smith|Johnson)) Full name: \1, First name: \2
# OPTIONAL TASK 2
#
# References can be used within the regex
# pattern (back references).
#
# Following program matches all 2-digit numbers
# with repeating digits (11, 22, 33, 44 .. 99).
#
# (\d)\1 Cute number! 🙂
#
# Extend this pattern for every numbers contain only repeating
# digits (11, 22, ... 111... 555)!
SCROLL DOWN FOR SOLUTIONS
⇩⇩⇩⇩⇩⇩⇩⇩⇩⇩⇩⇩⇩⇩⇩⇩⇩⇩⇩⇩⇩⇩⇩⇩⇩
# SOLUTION – TASK 1
#
# .*(..) \1
#
# or the less simple
#
# .*(.)(.) \1\2
# SOLUTION – TASK 2
#
# ([1-59]).* \1
# SOLUTION – TASK 3
#
# .*([^0][^0]) \1
# SOLUTION – TASK 4
#
# (\d\d\d).* \1
# SOLUTION – TASK 5
#
# NOTE: Last line will return with smaller and big numbers
# without changes:
#
# (\d{2,3})(\d{3}) \1,\2
# (\d{1,3})(\d{3})(\d{3}) \1,\2,\3
# (\d{1,3})(\d{3})(\d{3})(\d{3}) \1,\2,\3,\4
# .* \0
# SOLUTION – OPTIONAL TASK 1
# ((Anne|Becky) (Smith|Johnson)) Full name: \1, First name: \2
# expression replaces this way:
#
# Anne Smith -> Full name: Anne Smith, First name: Anne
# Becky Smith -> Full name: Becky Smith, First name: Becky
# Anne Johnson -> Full name: Anne Johnson, First name: Anne
# Becky Johnson -> Full name: Becky Johnson, First name: Becky
# SOLUTION – OPTIONAL TASK 2
#
# (\d)\1+ Cute number! 🙂
#######################################################
# CONGRATULATIONS – You have finished Tutorial Four! 🙂
#######################################################
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