How to resolve the algorithm Order by pair comparisons step by step in the Raku programming language

Published on 12 May 2024 09:40 PM
#Raku

How to resolve the algorithm Order by pair comparisons step by step in the Raku programming language

Table of Contents

Problem Statement

Assume we have a set of items that can be sorted into an order by the user. The user is presented with pairs of items from the set in no order, the user states which item is less than, equal to, or greater than the other (with respect to their relative positions if fully ordered). Write a function that given items that the user can order, asks the user to give the result of comparing two items at a time and uses the comparison results to eventually return the items in order. Try and minimise the comparisons the user is asked for. Show on this page, the function ordering the colours of the rainbow: The correct ordering being: Note:

Let's start with the solution:

Step by Step solution about How to resolve the algorithm Order by pair comparisons step by step in the Raku programming language

Source code in the raku programming language

my $ask_count = 0;
sub by_asking ( $a, $b ) {
    $ask_count++;
    constant $fmt = '%2d. Is %-6s [ less than | greater than | equal to ] %-6s? ( < = > ) ';
    constant %o = '<' => Order::Less,
                  '=' => Order::Same,
                  '>' => Order::More;

    loop {
        my $input = prompt sprintf $fmt, $ask_count, $a, $b;
        return $_ with %o{ $input.trim };
        say "Invalid input '$input'";
    }
}

my @colors = ;
my @sorted = @colors.sort: &by_asking;
say (:@sorted);

die if @sorted».substr(0,1).join ne 'roygbiv';
my $expected_ask_count = @colors.elems * log(@colors.elems);
warn "Too many questions? ({:$ask_count} > {:$expected_ask_count})" if $ask_count > $expected_ask_count;

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