By which I mean this:
Given the input set of numbers:
1,2,3,4,5 becomes \"1-5\".
1,2,3,5,7,9,10,11,12,14 becomes \"1-3, 5, 7, 9-12, 14\"
This is
Short and sweet Ruby
def range_to_s(range)
return range.first.to_s if range.size == 1
return range.first.to_s + "-" + range.last.to_s
end
def format_ints(ints)
range = []
0.upto(ints.size-1) do |i|
range << ints[i]
unless (range.first..range.last).to_a == range
return range_to_s(range[0,range.length-1]) + "," + format_ints(ints[i,ints.length-1])
end
end
range_to_s(range)
end
Looks clear and straightforward to me. You can simplify a bit if you either assume the input array is sorted, or sort it yourself before further processing.
The only tweak I'd suggest would be to reverse the subtraction:
int difference = (current - lastNumber);
... simply because I find it easier to work with positive differences. But your code is a pleasure to read!
Here's my Haskell entry:
runs lst = map showRun $ runs' lst
runs' l = reverse $ map reverse $ foldl newOrGlue [[]] l
showRun [s] = show s
showRun lst = show (head lst) ++ "-" ++ (show $ last lst)
newOrGlue [[]] e = [[e]]
newOrGlue (curr:other) e | e == (1 + (head curr)) = ((e:curr):other)
newOrGlue (curr:other) e | otherwise = [e]:(curr:other)
and a sample run:
T> runs [1,2,3,5,7,9,10,11,12,14]
["1-3","5","7","9-12","14"]
With input validation/pre-sorting
You can easily get the result as a LoL if you need to do something more fancy than just return a string.
#!/usr/bin/perl -w
use strict;
use warnings;
use Scalar::Util qw/looks_like_number/;
sub adjacenify {
my @input = @_;
# Validate and sort
looks_like_number $_ or
die "Saw '$_' which doesn't look like a number" for @input;
@input = sort { $a <=> $b } @input;
my (@output, @range);
@range = (shift @input);
for (@input) {
if ($_ - $range[-1] <= 1) {
push @range, $_ unless $range[-1] == $_; # Prevent repetition
}
else {
push @output, [ @range ];
@range = ($_);
}
}
push @output, [ @range ] if @range;
# Return the result as a string. If a sequence is size 1, then it's just that number.
# Otherwise, it's the first and last number joined by '-'
return join ', ', map { 1 == @$_ ? @$_ : join ' - ', $_->[0], $_->[-1] } @output;
}
print adjacenify( qw/1 2 3 5 7 9 10 11 12 14/ ), "\n";
print adjacenify( 1 .. 5 ), "\n";
print adjacenify( qw/-10 -9 -8 -1 0 1 2 3 5 7 9 10 11 12 14/ ), "\n";
print adjacenify( qw/1 2 4 5 6 7 100 101/), "\n";
print adjacenify( qw/1 62/), "\n";
print adjacenify( qw/1/), "\n";
print adjacenify( qw/1 2/), "\n";
print adjacenify( qw/1 62 63/), "\n";
print adjacenify( qw/-2 0 0 2/), "\n";
print adjacenify( qw/-2 0 0 1/), "\n";
print adjacenify( qw/-2 0 0 1 2/), "\n";
Output:
1 - 3, 5, 7, 9 - 12, 14
1 - 5
-10 - -8, -1 - 3, 5, 7, 9 - 12, 14
1 - 2, 4 - 7, 100 - 101
1, 62
1
1 - 2
1, 62 - 63
-2, 0, 2
-2, 0 - 1
-2, 0 - 2
-2, 0 - 2
And a nice recursive solution:
sub _recursive_adjacenify($$);
sub _recursive_adjacenify($$) {
my ($input, $range) = @_;
return $range if ! @$input;
my $number = shift @$input;
if ($number - $range->[-1] <= 1) {
return _recursive_adjacenify $input, [ @$range, $number ];
}
else {
return $range, _recursive_adjacenify $input, [ $number ];
}
}
sub recursive_adjacenify {
my @input = @_;
# Validate and sort
looks_like_number $_ or
die "Saw '$_' which doesn't look like a number" for @input;
@input = sort { $a <=> $b } @input;
my @output = _recursive_adjacenify \@input, [ shift @input ];
# Return the result as a string. If a sequence is size 1,
# then it's just that number.
# Otherwise, it's the first and last number joined by '-'
return join ', ', map { 2 == @$_ && $_->[0] == $_->[1] ? $_->[0] :
1 == @$_ ? @$_ :
join ' - ', $_->[0], $_->[-1] } @output;
}
See How would you display an array of integers as a set of ranges? (algorithm)
My answer to the above question:
void ranges(int n; int a[n], int n)
{
qsort(a, n, sizeof(*a), intcmp);
for (int i = 0; i < n; ++i) {
const int start = i;
while(i < n-1 and a[i] >= a[i+1]-1)
++i;
printf("%d", a[start]);
if (a[start] != a[i])
printf("-%d", a[i]);
if (i < n-1)
printf(",");
}
printf("\n");
}
Pure functional Python:
#!/bin/env python
def group(nums):
def collect((acc, i_s, i_e), n):
if n == i_e + 1: return acc, i_s, n
return acc + ["%d"%i_s + ("-%d"%i_e)*(i_s!=i_e)], n, n
s = sorted(nums)+[None]
acc, _, __ = reduce(collect, s[1:], ([], s[0], s[0]))
return ", ".join(acc)
assert group([1,2,3,5,7,9,10,11,12,14]) == "1-3, 5, 7, 9-12, 14"