Why not adapt the solution ikegami suggested a few weeks back on the Near equal partitions. thread?
sub ranges_beth2 {
my ($M, $N) = @_;
my $r = ($M+1)%$N;
my $q = ($M+1-$r)/$N;
my $iEnd=0;
return [ map { my $iStart=$iEnd; [$iStart, ($iEnd+=$_) - 1]
} (($q+1) x $r, ($q) x ($N-$r)) ];
}
Sample output
---------------------------
0 : from 0 to 9999997 (9999998)
---------------------------
0 : from 0 to 4999998 (4999999)
1 : from 4999999 to 9999997 (4999999)
---------------------------
0 : from 0 to 3333332 (3333333)
1 : from 3333333 to 6666665 (3333333)
2 : from 6666666 to 9999997 (3333332)
---------------------------
0 : from 0 to 2499999 (2500000)
1 : from 2500000 to 4999999 (2500000)
2 : from 5000000 to 7499998 (2499999)
3 : from 7499999 to 9999997 (2499999)
It ensures that partitions never differ by more than 1 in size and avoids rounding errors. On benchmark results it is also marginally faster (4-8%) than the code in the OP (actual result varies between runs)
s/iter buk eli_ik
buk 1.01 -- -8%
eli_ik 0.923 9% --
Rate buk eli_ik
buk 1.02/s -- -4%
eli_ik 1.06/s 4% --
Benchmark code
use Benchmark qw(cmpthese);
sub testRanges {
my $cr=$_[0];
for my $M (1..1e2) {
for my $N (1..$M) {
$cr->($M,$N);
}
}
}
cmpthese(10
, { 'buk' => sub { testRanges(\&ranges_buk) }
, 'eli_ik' => sub { testRanges(\&ranges_beth2) }
}
);
Update: added that it avoids rounding errors.
Update: minor revision to account for OP desiring range to go from 0..$M ($M+1 values) not 0..($M-1), i.e. $M values.
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