Singleton-Filter-But-Preserving-Order
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#!/usr/bin/env raku
#| The program outputs the numbers that appear only once in the input - keeping the original order
# example input
#2
#1
#4
#3
#2
#1
# expected output for the example input
#4
#3
# read all lines from standard input - we need it twice, hence we store it in an array
my @numbers = $*IN.lines;
# find numbers that appear only once
my @singletons = @numbers.Bag.grep(*.value == 1).map(*.key);
# print the single-occurrence numbers in their original order
@numbers.grep( * ∈ @singletons ).join("\n").put
Raku
INFO