input: Write a function to optimize the following Python code to sort a set of numbers (set = [2, 6, 3, 8, 4]) in O(n) time complexity. The function should accept an unsorted list as input and return the sorted list.
  
  assert sort_list([2, 6, 3, 8, 4])==[2, 3, 4, 6, 8]
  assert sort_list([9, 1, 5, 7, 3])==[1, 3, 5, 7, 9]
  assert sort_list([10, 20, 30, 40, 50])==[10, 20, 30, 40, 50]
  assert sort_list([])==[]
  assert sort_list([1])==[1]
output: def sort_list(nums):
      if not nums:
          return nums
      max_val = max(nums)
      count = [0] * (max_val + 1)
      for num in nums:
          count[num] += 1
      sorted_list = []
      for i in range(max_val + 1):
          sorted_list.extend([i] * count[i])
      return sorted_list