I'm trying to create a function that checks if two numbers within an array have a sum of zero.
[1,2,3,4,5] => false
[1,2,3,-2,5] => true
This is what I have so far but I can't figure it out:
def zero_sum?(arr)
arr.each do |num|
arr.each do |num2|
if (num.to_i + num2.to_i) == 0
true
else
false
end
end
end
end
You want to know whether any combination of 2 elements adds up to zero. You can pretty much write that down verbatim:
arr.combination(2).any? {|a, b| (a + b).zero? }
combination doesn't mix two array elements of the same index, which is why a single 0 yields false.
true and false symmetrically), so it cannot be relied on. I also took the wording.
Enumerable is basic Ruby. In fact, it solves pretty much 80% of all basic programming problems.You need return true instead of true.
This way, the value in the block is true when it needs to be, but the looping continues, and finally each returns arr.
Also, can be written shorter, but it is not as efficient:
def zero_sum?(arr)
arr.product(arr).any? { |x, y| x + y == 0 }
end
A bit less nice but efficient:
def zero_sum?(arr)
arr.product(arr) { |x, y| return true if x + y == 0 }
false
end
an easy way to do it is:
def zero_sum?(arr)
arr.count(0) > 1 or
arr.-([0]).any?{|e| arr.include?(-e)}
end
arr.-([]) was until I removed the dot and found it made no difference. As the parens are just to avoid ]., it's the same as (arr-[0]). You could also use arr.uniq, but that would be less descriptive.another way to do this:-
array.product(array).any?{|arr| arr.sum.zero?}
arr.count(0) > 1 or
arr.uniq.map(&:abs).group_by(&:to_i).values.map(&:size).max > 0
I really don't think this is the best answer, but it might be of interest to someone. (Borrowed part before or from @sawa.)
arr.each_cons(2).select{|array|array.inject(:+) == 0}.count > 0
