Rosalind: SUBS failing the given case

I wrote a solution to this challenge based on this answer. It successfully handles the example case given, but not the actual case.

Challenge:

Given two strings s and t, t is a substring of s if t is contained as a contiguous collection of symbols in s (as a result, t must be no longer than s).

The position of a symbol in a string is the total number of symbols found to its left, including itself (e.g., the positions of all occurrences of 'U' in "AUGCUUCAGAAAGGUCUUACG" are 2, 5, 6, 15, 17, and 18). The symbol at position i of s is denoted by s[i].

A substring of s can be represented as s[j:k], where j and k represent the starting and ending positions of the substring in s; for example, if s = "AUGCUUCAGAAAGGUCUUACG", then s[2:5] = "UGCU".

The location of a substring s[j:k] is its beginning position j; note that t will have multiple locations in s if it occurs more than once as a substring of s (see the Sample below).

Given:

Two DNA strings s and t (each of length at most 1 kbp).

Return:

All locations of t as a substring of s.

Sample Dataset:

GATATATGCATATACTT
ATAT

Sample Output:

2 4 10

For the sample, it works. Sure, you need to trim the formatting by hand, but that's only a couple of seconds of work.

The actual data and my generated output are not accepted.

Actual Dataset:

CAAATAGTCACACAATAGTCGGCTAAATAGTCAATAGTCAAATAGTCAGAGCTAATAGTCTAAATAGTCGAAAAATAGTCATCAATAGTCTAAATAGTCAATAGTCGGAATAGTCAAAATAGTCAATAGTCAATAGTCAATAGTCGACTAAATAGTCCCAATAGTCTCAGAAATAGTCAATAGTCGTAATAGTCAATAGTCTAATAGTCTAATAGTCCAATAGTCTGTCAAATAGTCAATAGTCCAATAGTCGTTTAATAGTCCCCTTTACCAATAGTCAATAGTCCGAATAGTCAGGAATAGTCAGCACTAATAGTCAATAGTCCTAATAGTCCCAATAGTCAAAATAGTCAATAGTCTAAATAATAGTCCTAGCAGAAGAATAGTCTAATAGTCGGCAATAGTCAATAGTCAAATAGTCAGAATAGTCAAATAGTCGAAATAGTCAATAGTCAATAGTCAAATAGTCAAATAGTCAATAGTCAAATAGTCAAATAGTCAAATAGTCGAATAGTCTGTAATAGTCAATAGTCCTTCAATAGTCTAATAGTCATTCAATAGTCAAGAAATAGTCGGGGGAATAGTCCGAATAGTCAAATAGTCAATAGTCGAATAGTCTAATAGTCAATAGTCTAATAGTCTGATAATAGTCAAATAGTCAATAGTCTAAATAGTCGCCTATGCCAATAGTCTTATCAAATAGTCTCTTAATAGTCTAATAGTCAATAGTCAATAGTCTAATAGTCATAATAGTCAATAGTCAAGGAATAGTCCCATAATAGTCAATAGTCTTAATAGTCCAAACGAAATAGTCTTAATAGTCCCTAATAGTCACTAATAGTCGTAATAGTCATAATAGTCCAATAGTCTAAATAGTCTGCAATAGTCAAATAGTCAAATAGTCCGTACAATAGTCTTAATAGTCTTTGCGGCTCAATAGTCTCATAATAGTC
AATAGTCAA

Actual Output (trimmed):

26 33 93 109 118 125 132

Code:

def find_substring_locations(long, short)
  mpos = []
  re = Regexp.new(short)
  m = i = 0
  m = re.match( long, i ) { |k| j = k.begin(0); i = j + 1; mpos << j } while m
  return mpos
end

def plus_one(input)
  arr = []
  for i in input
    arr << (i += 1)
  end
  arr
end

main_string = gets.chomp
sub_string = gets.chomp
plus_one(find_substring_locations(main_string, sub_string))

Where did I go wrong? It appears to be in order.

EDIT: Turns out the problem was a hiccup in the environment. After a reboot the problem could not be reproduced.

I think your code is correct besides an off by one error. The plus_one solution can be simplified.

m = re.match( long, i ) { |k| j = k.begin(0); i = j + 1; mpos << j + 1} while m

But there is an easier way to implement. You don't need the Regexp, there is an easier way to search for the index of a substring match:

String#index takes an additional argument, the starting index.

input = "CAAATAGTCACACAATAGTCGGCTAAATAGTCAATAGTCAAATAGTCAGAGCTAATAGTCTAAATAGTCGAAAAATAGTCATCAATAGTCTAAATAGTCAATAGTCGGAATAGTCAAAATAGTCAATAGTCAATAGTCAATAGTCGACTAAATAGTCCCAATAGTCTCAGAAATAGTCAATAGTCGTAATAGTCAATAGTCTAATAGTCTAATAGTCCAATAGTCTGTCAAATAGTCAATAGTCCAATAGTCGTTTAATAGTCCCCTTTACCAATAGTCAATAGTCCGAATAGTCAGGAATAGTCAGCACTAATAGTCAATAGTCCTAATAGTCCCAATAGTCAAAATAGTCAATAGTCTAAATAATAGTCCTAGCAGAAGAATAGTCTAATAGTCGGCAATAGTCAATAGTCAAATAGTCAGAATAGTCAAATAGTCGAAATAGTCAATAGTCAATAGTCAAATAGTCAAATAGTCAATAGTCAAATAGTCAAATAGTCAAATAGTCGAATAGTCTGTAATAGTCAATAGTCCTTCAATAGTCTAATAGTCATTCAATAGTCAAGAAATAGTCGGGGGAATAGTCCGAATAGTCAAATAGTCAATAGTCGAATAGTCTAATAGTCAATAGTCTAATAGTCTGATAATAGTCAAATAGTCAATAGTCTAAATAGTCGCCTATGCCAATAGTCTTATCAAATAGTCTCTTAATAGTCTAATAGTCAATAGTCAATAGTCTAATAGTCATAATAGTCAATAGTCAAGGAATAGTCCCATAATAGTCAATAGTCTTAATAGTCCAAACGAAATAGTCTTAATAGTCCCTAATAGTCACTAATAGTCGTAATAGTCATAATAGTCCAATAGTCTAAATAGTCTGCAATAGTCAAATAGTCAAATAGTCCGTACAATAGTCTTAATAGTCTTTGCGGCTCAATAGTCTCATAATAGTC"
query = "AATAGTCAA"

def substring_index(input, query)
  last = 0
  matches = []

  while index = input.index(query, last) do
    matches << index += 1
    last = index
  end
  matches
end


p substring_index(input, query)
# => [26, 33, 93, 109, 118, 125, 132, 172, 188, 231, 273, 312, 337, 346, 400, 407, 424, 441, 448, 455, 463, 471, 478, 486, 494, 520, 557, 589, 597, 620, 646, 654, 718, 725, 749, 756, 778, 882, 890]