The Code Golf Game

[Europe2048]

Post a solution to the LeetCode problem with the number one more than the previous (unless rule 7 says otherwise), in a language x chosen by the user.
Rules:

• No double-posting!
• The x of a post may not be the same as the x of the last post.
• The next solution's length (in characters) must be shorter than that of the previous.
• The x may not be an esolang made by you, or an esolang made to solve the problem in the fewest characters. If the language supports custom libraries, don't make a library to solve the problem in the fewest characters. In other words, no cheating.
• Please state the programming language you used and the number of the problem solved in the message.
• The code must be written in a function called sol, whenever possible.
• If a problem is only for premium and you don't have it, don't waste your money. Skip that problem.
• If you think it's impossible to advance, restart from Problem 1 (Two Sum).
• If you think it's impossible to advance with the O(___) restriction given, ignore that restriction.

I'll start.

Python (1)

Code Select Expand

def sol(nums):
        a = []
        for i in range(0, len(nums)):
            for j in range(0, len(nums)):
                if i == j:
                    pass
                elif nums[i] + nums[j] == target:
                    a.append(i)
                    a.append(j)
        return list(set(a))

[PkmnQ]

Haskell, 179 chars (2)

Code Select Expand

s 0 [] ys = ys
s 0 xs [] = xs
s c [] ys = s 0 [c] ys
s c xs [] = s 0 xs [c]
s c (x:xs) (y:ys) = let z = x + y + c in if z < 10 then z : s 0 xs ys else z - 10 : s 1 xs ys
sol = s 0Try it online!

Could've made it shorter, but it's already short enough anyway
I chose Haskell because I couldn't bother finding another linked list implementation
Also, is J allowed? It's not an esolang and I don't think it was made to be as short as possible, but it's also ridiculously good at being short due to its syntax
And what about double posting? I probably won't do it that much but I will for bumping

For convenience: https://leetcode.com/problemset/

[Gilbert189]

You want brief? I can brief.
APL (Dyalog Extended), 70 bytes (3)

Code Select Expand

sol←{≢⊃(⌽/∘i)(∪≡⊢)¨(i←{⍵⊂⍛⌷s}¨{↑,/⍵{(⍺-⍵-1)({¯1+⍳⍺}+⊢⍤/)⊂⍳⍵}¨⍳⍵}≢s←⍵)}
Try it online!

If I was smarter on the trains, I could probably shave 3 or 4 bytes or something.

Edit since misconceptions are imminent: FYI, both the APLers and most of the esolangers never considered APL an esolang, and I'm not sure if "writing concise code" was what APL was made for or just a side effect of being so rich in features

[Europe2048]

To PkmnQ: Yes, J is allowed. J is not that kind of esolang where you type a number to solve problem number n.

(This reply has no effect on gameplay)

[PkmnQ]

[ngv]This is definitely possible (ignoring the O(_) restriction), but I think I chose possibly the most painful option that it's possible to do with[/ngv]