Sorted them both

Weekly challenge 217 — 15 May 2023

Week 217 - 15 May 2023

Task 2

You are given a list of positive integers. Write a script to concatenate the integers to form the highest possible value.

This is a rather frustrating problem in that it's hard to see a simple alternative to just trying all possible concatenations. I have done that using recursion, which has the usual issue of being quite slow when the number of numbers exceeds, in this case, around 9.

It would be faster using one of the modules that generates permutations, but my free web hosting doesn't have those installed and doesn't allow me access to cpan, and I don't have time to write one myself.

#!/usr/bin/perl use v5.16; # The Weekly Challenge - 2023-05-15 use utf8; # Week 217 task 2 - Max number use strict; # Peter Campbell Smith use warnings; # Blog: http://ccgi.campbellsmiths.force9.co.uk/challenge max_number(1, 23); max_number(10, 3, 2); max_number(31, 2, 4, 10); max_number(5, 11, 4, 1, 2); max_number(1, 10); max_number(9900, 1, 99, 88); max_number(47, 53, 99, 82, 9, 21, 36, 76, 77); sub max_number { my (%left, $max); # put the numbers in a hash (as keys) $left{$_} = 1 for @_; # show result say qq[\nInput: (] . join(', ', @_) . ')'; say qq[Output: ] . add_a_number(0, '', \%left); } sub add_a_number { my ($max, $so_far, $so_far2, %left, %more, $this); # initialise $max = $_[0]; $so_far = $_[1]; %left = %{$_[2]}; # added all numbers unless (%left) { $max = $so_far if $so_far > $max; # add the next number } else { for $this (keys %left) { %more = %left; delete $more{$this}; $max = add_a_number($max, $so_far . $this, \%more); } } # return the best so far return $max; }

Input: (1, 23) Output: 231 Input: (10, 3, 2) Output: 3210 Input: (31, 2, 4, 10) Output: 431210 Input: (5, 11, 4, 1, 2) Output: 542111 Input: (1, 10) Output: 110 Input: (9900, 1, 99, 88) Output: 999900881 Input: (47, 53, 99, 82, 9, 21, 36, 76, 77) Output: 99982777653473621

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Peter Campbell Smith is hereby placed in the public domain