Ruby variable not working properly in function

Question

I have this function:

def find_deleted_number(arr, mixed_arr)

    default = 0

    arr.each do |i|
        if mixed_arr.include?(arr[i]) == true
            default += arr[i]
        else 
            return arr[i]
        end
    end
    return default  
end

find_deleted_number([1,2,3,4,5], [3,4,1,5])
#=> 2 (as expected)

find_deleted_number([1,2,3,4,5,6,7,8,9], [1,9,7,4,6,2,3,8])
#=> 5 (as expected)

find_deleted_number([1,2,3,4,5,6,7,8,9], [5,7,6,9,4,8,1,2,3])
#=> nil (expected 45)

The idea is for the function to check which number is in arr but not in mixed_arr. That's all good but the problem is that when both arrays are the same, I want it to give me the sum of every value in one of the arrays (that's why I do default += arr[i]). But the result is nil and I dont quite understand why. If possible I would like to understand the reason why it is failing.

What do you expect from this case: find_deleted_number([1,2,3,4,5,6,7,8,9,9], [5,7,6,9,4,8,1,2,3])? Note the repeated 9. Of course if this case was a possible input. — iGian
– iGian, Commented Mar 16, 2021 at 9:13

yzalavin · Accepted Answer · 2021-03-16 07:04:08Z

3

arr.each iterates over elements of arr, not over indexes. Therefore, you need to change arr[i] to i.

The full answer is:

def find_deleted_number(arr, mixed_arr)
  default = 0

  arr.each do |i|
    if mixed_arr.include?(i)
      default += i
    else 
      return i
    end
  end

  default  
end

answered Mar 16, 2021 at 7:04

yzalavin

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Comments

eux · Accepted Answer · 2021-03-16 07:29:34Z

2

The reason why it is failing as @yzalavin said.

You could also simplify your code:

def find_deleted_number(arr, mixed_arr)
  return arr.sum if arr.sort == mixed_arr.sort

  (arr - mixed_arr).first
end

And @Stefan provide an even shorter one-liner:

(arr - mixed_arr).first || arr.sum

edited Mar 16, 2021 at 7:29

answered Mar 16, 2021 at 7:08

eux

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4 Comments

Stefan Over a year ago

Even shorter: (arr - mixed_arr).first || arr.sum

eux Over a year ago

@Stefan Wow impressive : )

Cary Swoveland Over a year ago

Suppose arr = [1,2]; mixed = [1,2,3]. Then arr.sort == mixed_arr.sort #=> false, so (arr - mixed_arr).first #=> [].first #=> nil is returned, which is incorrect.

eux Over a year ago

@CarySwoveland Yeah, this just works within condition: The idea is for the function to check which number is in arr but not in mixed_arr.

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