sub is-touching(@H, @T --> Bool:D) {
so (@H[0] - @T[0]) & (@H[1] - @T[1]) == -1|0|1
}
sub simulate(@movements, UInt:D \knot-num--> UInt:D) {
my @knots = [0, 0] xx knot-num;
my %trail is SetHash;
for @movements -> \drt, \dst {
for 1 .. dst.Int {
given drt {
when 'U' { ++@knots[0;1] }
when 'D' { --@knots[0;1] }
when 'L' { --@knots[0;0] }
when 'R' { ++@knots[0;0] }
}
for 1 ..^ knot-num -> \k {
unless is-touching(@knots[k-1], @knots[k]) {
@knots[k;0] += (@knots[k-1;0] - @knots[k;0]).sign;
@knots[k;1] += (@knots[k-1;1] - @knots[k;1]).sign;
}
}
%trail.set("{ @knots[knot-num - 1; 0] }:{ @knots[knot-num - 1;1] }");
}
}
+%trail
}
with $*IN.words -> @movements {
put 'part 1: ', simulate(@movements, 2);
put 'part 2: ', simulate(@movements, 10);
}
