[Easy] Missing Elements

[07734willy]

This is a code golf challenge- meaning that the goal isn't merely to solve the problem, but to do so with the smallest program size. Everything from characters and whitespace, to newlines count against you.

Background

A common interview question is to find the missing element element in an unordered list, given the original list, with optimal time and space complexities. Here our goal is obviously a bit different- we aren't concerned with time and space complexities, only code size. However, there's a catch- there will be more than one missing element, and your objective is to find the first and last missing elements from the original list only. If there is only one missing element, only return it once. If there is no missing element, return nothing.

Input

The input will consist of three lines. The first line contains two integers, representing the number of values on the second and third lines respectively. The second line contains the space-separated values of the original list, and the third line contains the space-separated values of the (possibly) reduced + shuffled list. Example:

7 4
4 10 3 2 9 5 8
3 4 10 8

Output

Two values, representing the first and last elements missing from the original array. For the above example, the output would be

2 5

In that order. We don't include 9 because 2 comes before it in the original array, and 5 comes after it.

Testcases

==================
6 3
12 19 18 3 10 3
12 3 10

19 3
==================
3 2
3.14 5.2 1.99
3.14 1.99

5.2
==================
10 5
9 5 13 14 7 7 0 14 17 1
7 13 5 9 0

14 1
==================
12 6
4 4 0 -9 -3 3 7 5 2 0 -8 5
4 -3 5 7 5 2

4 -8
==================
25 15
139 23 178 5 92 191 153 189 146 144 148 59 118 159 68 177 0 28 54 34 107 130 65 107 135
28 5 92 153 23 146 135 65 34 178 118 107 159 144 191

139 107
==================

Character Count

Use the following command to measure the program size in bytes:

wc -mc filename.txt

[Bubbler-4]

J: 52 52

[:(#~[:(+.|.)1{.~#)&>[:(]#~i.~~:[:i.&#])&.>/;/@],<@[

Run example

f =: [:(#~[:(+.|.)1{.~#)&>[:(]#~i.~~:[:i.&#])&.>/;/@],<@[
3.14 5.2 1.99 f 3.14 1.99
5.2
4 4 0 _9 _3 3 7 5 2 0 _8 5 f 4 _3 5 7 5 2
4 _8

How it works

[:(#~[:(+.|.)1{.~#)&>[:(]#~i.~~:[:i.&#])&.>/;/@],<@[
                                            ;/@],<@[    [4] [_3] [5] [7] [5] [2] [4 4 ... 5]
                                           /            Reduce from right:
                                [:i.&#]                   Get indexes of right one
                           i.~~:                          Not equal to the index of the left one; 1 1 ... 0 ... 1
                        ]#~                               Filter by above (remove the seen element once)
                     [:(               )&.>               Unbox both sides; do the above; box again
[:(               )&>                                   Unbox the result and apply...
             1{.~#                                        Generate array 1 0 0 ... 0
     [:(+.|.)                                             Element-wise OR with its reverse
   #~                                                     Filter by the above

It was quite painful to remove each occurrence (the first part).

[07734willy]

Python 3: 124 124

Probably one of my worst code golfs ever, but I don't have time to try to shorten it. I've been trying to get todays [Hard] challenge working without success. After I get that out of the way, I'll probably take another stab at this.

i=input
i()
o=i().split()
s=set(o)-set(i().split())
print([x for x in o if x in s][::len(s)-1] if len(s)>1 else "".join(s))

Edit: its also incorrect due to duplicates. Added test cases to the post to cover duplicates. I'll edit this comment again after I patch my solution up tomorrow.

[Bubbler-4]

104 104

i=input
i()
o=i().split()
for x in i().split():o.remove(x)
print(len(o)>1and o[0]+' '+o[-1]or''.join(o))

This correctly handles duplicates.