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Project Euler 159

mscha Mar 11th, 2017 (edited) 160 Never
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  1. #!/usr/bin/env perl6
  2.  
  3. # Solution for Project Euler problem 159
  4. # https://projecteuler.net/problem=159
  5.  
  6. use v6.c;
  7.  
  8. sub MAIN(Int $limit = 10, Bool :v(:$verbose) = False)
  9. {
  10.     my $max = $limit - 1;
  11.  
  12.     # Start with the digital roots of 1..max
  13.     # The digital root of n > 0 is just (n mod 9) || 9, so generate a list
  14.     # of repeated 1..9s of exactly the right length
  15.     my @mdsr = 0, |(|(1..9) xx ($max div 9)), |(1..($max % 9));
  16.     say @mdsr if $verbose;
  17.  
  18.     # mdsr(n) = max(dr(n), mdsr(i) + mdsr(j)) for all i > j > 1 with n = i×j
  19.     # so loop over all i and j and update mdsr(i×j) where necessary
  20.     #for 2 .. ($max div 2) -> $i {
  21.     loop (my $i = 2, my $max-i = $max div 2; $i <= $max-i; $i++) {
  22.         #for 2 .. ($max div $i) -> $j {
  23.         loop (my $j = 2, my $max-j = $max div $i; $j <= $max-j; $j++) {
  24.             @mdsr[$i*$j] max= @mdsr[$i] + @mdsr[$j];
  25.         }
  26.         say "$i: ", @mdsr if $verbose;
  27.     }
  28.  
  29.     # We need the sum from 2..limit, so subtract @mdsr[0]=0 and @mdsr[1]=1
  30.     say “∑mdrs(n) for 1 < n < $limit is:, @mdsr.sum - 1;
  31. }
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