From: "Eric I." <rubytraining@...>
Date: 2007-07-15T23:50:00+09:00
Subject: Re: Maximum Sub-Array (#131) [SOLUTION]

I went for the all-in-one line solution (not including the method
definition boilerplate), with no consideration for the computational
or memory cost.  Here are two versons, the first does not require the
'enumerator' library, the second does and is slightly shorter as a
result.  Both will favor shorter solutions over longer solutions if
they have the same sum.

In both cases the code generates every possible sub-array and sorts
them by two factors: 1) sum of elements ascending, and 2) size of sub-
array descending.  Finally it chooses the solution at the end of this
sorted list.

In the first solution, it generates every sub-array by using all
possible combinations of starting and ending indices.

def max_sub_array(a)
  (0...a.size).inject([]) { |c, s| c + (s...a.size).map { |e|
a.slice(s..e) } }.sort_by { |b| [b.inject { |s, e| s + e }, -
b.size] }.last
end

In the second solution, it generates every sub-array by sequencing
through all possible sub-array lengths (1..size) and then calling
enum_cons.  If you're not familiar with enum_cons, it takes a size as
a parameter and returns an Enumerable for every sub-array of that size
(e.g., [1, 2, 3, 4].enum_cons(2) would provide an Enumerable that
would encode the sequence [1, 2], [2, 3], and [3, 4]).

def max_sub_array2(a)
  (1..a.size).inject([]) { |l, s| l + a.enum_cons(s).to_a }.sort_by { |
b| [b.inject { |s, e| s + e }, -b.size] }.last
end

Eric

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