How to use a 'two pointer' algorithm in Elixir

Questions & Help Questions
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1

I’m learning Elixir with Leetcode.

The Leetcode problem is Valid Triangle Number.

My Rust solution uses two pointers with array

impl Solution {
    pub fn triangle_number(mut nums: Vec<i32>) -> i32 {
        nums.sort();
        let mut ans = 0;
        for i in 2..nums.len() {
            let mut left = 0;
            let mut right = i - 1;
            while left < right {
                if nums[left] + nums[right] > nums[i] {
                    ans += right - left;
                    right -= 1;
                } else {
                    left += 1;
                }
            }
        }
        ans as i32
    }
}

I got Timeout when I trying to convert this code to Elixir.

defmodule Solution do
  @spec triangle_number(nums :: [integer]) :: integer
  def triangle_number(nums) do
     len = Enum.count(nums)
     if len < 3 do
        0
     else
        nums |> Enum.sort |> loop_nums(2, len)
     end
  end
  
  def loop_nums(nums, i, len) do
      if i == len do
         0
      else
         check_intervals(nums, 0, i - 1, i) + loop_nums(nums, i + 1, len)
      end
  end
  
  def check_intervals(nums, a, b, c) do
      cond do
          a >= b -> 0
          Enum.at(nums, a) + Enum.at(nums, b) > Enum.at(nums, c) -> b - a + check_intervals(nums, a, b - 1, c)
          true -> check_intervals(nums, a + 1, b, c)
      end 
  end 
end

How to improve the performance?

Thank you.