require 'set'
# Finds the last repeated character in a string.
# Scans the string from right to left using a Set to track seen characters.
# Returns the character, or nil if no characters are repeated.
def find_last_repeated_character(str)
seen = Set.new
# Iterate through the string's characters in reverse order (right to left)
str.chars.reverse_each do |char|
# Set#add? returns nil if the element is already present in the set.
# This efficiently checks for existence and adds the element in one step.
return char unless seen.add?(char)
end
nil
end
# Test cases adapted from your C++ examples
test_cases = [
"abca",
"abcbd",
"abcde",
"abcdxypcbop",
"abcdxypcbadom"
]
test_cases.each do |tc|
result = find_last_repeated_character(tc)
# Print ' ' if nil, mirroring the C++ ternary expression (result ? result : ' ')
output = result ? result : ' '
puts "findLastRepeatedCharacter(#{tc.inspect}) -> #{output}"
end
# run:
#
# findLastRepeatedCharacter("abca") -> a
# findLastRepeatedCharacter("abcbd") -> b
# findLastRepeatedCharacter("abcde") ->
# findLastRepeatedCharacter("abcdxypcbop") -> p
# findLastRepeatedCharacter("abcdxypcbadom") -> d
#
