Sum of two elements of a list equaling a target In effort to learn OCaml, I'm going through some easy LeetCode problems and attempting to implement them. I arrive at the correct answer, but I'm still developing an intuition for canonical OCaml code. I'd appreciate any feedback on my implementation.

As mentioned, this is problem 1 on LeetCode. A quick summary of the problem: given an array of integers, return the indices of the 2 numbers that sum to a given "target".

For example, given nums: [2, 7, 11, 15] and target: 13, the result should be [0, 2] (the integers at indices 0 and 2 sum to 13).

Furthermore, we can assume a unique solution exists for the given array and target.

Here is my refined attempt at implementing this in OCaml:

let two_sum nums target =
  let rec aux i j =
    let n1 = List.nth nums i in
    let n2 = List.nth nums j in
      if n1 + n2 = target then [i; j]
      else if j = (List.length nums) - 1 then aux (i + 1) (i + 2)
      else aux i (j + 1)
  in aux 0 1;;


I appreciate any feedback.
Since the task is about using arrays, I would suggest to use OCaml arrays and not list. Because of lists, you need to use List.nth and that is quite costly.