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Ingy döt Net 2023-07-01 11:58:00 -04:00
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commit cb5bb5e222
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Task/Closest-pair-problem/Raku/closest-pair-problem.raku Normal file
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sub MAIN ($N = 5000) {
my @points = (^$N).map: { [rand × 20 - 10, rand × 20 - 10] }
my @candidates = @points.sort(*.[0]).rotor( 10 => -2, :partial).race.map: { closest-pair-simple(@$_) }
say 'simple ' ~ (@candidates.sort: *.[2]).head(1).gist;
@candidates = @points.sort(*.[0]).rotor( 10 => -2, :partial).race.map: { closest-pair(@$_) }
say 'real ' ~ (@candidates.sort: *.[2]).head(1).gist;
}
sub dist-squared(@a, @b) { (@a[0] - @b[0])² + (@a[1] - @b[1])² }
sub closest-pair-simple(@points is copy) {
return ∞ if @points < 2;
my ($a, $b, $d) = |@points[0,1], dist-squared(|@points[0,1]);
while @points {
my \p = pop @points;
for @points -> \l {
($a, $b, $d) = p, l, $_ if $_ < $d given dist-squared(p, l);
}
}
$a, $b, $d.sqrt
}
sub closest-pair(@r) {
closest-pair-real (@r.sort: *.[0]), (@r.sort: *.[1])
}
sub closest-pair-real(@rx, @ry) {
return closest-pair-simple(@rx) if @rx ≤ 3;
my \N = @rx;
my \midx = ceiling(N/2) - 1;
my @PL := @rx[ 0 .. midx];
my @PR := @rx[midx+1 ..^ N ];
my \xm = @rx[midx;0];
(.[0] ≤ xm ?? my @yR !! my @yL).push: @$_ for @ry;
my (\al, \bl, \dL) = closest-pair-real(@PL, @yR);
my (\ar, \br, \dR) = closest-pair-real(@PR, @yL);
my ($w1, $w2, $closest) = dR < dL ?? (ar, br, dR) !! (al, bl, dL);
my @yS = @ry.grep: { (xm - .[0]).abs < $closest }
for 0 ..^ @yS -> \i {
for i+1 ..^ @yS -> \k {
next unless @yS[k;1] - @yS[i;1] < $closest;
($w1, $w2, $closest) = |@yS[k, i], $_ if $_ < $closest given dist-squared(|@yS[k, i]).sqrt;
}
}
$w1, $w2, $closest
}