input: Write a function to find the minimum subarray length whose sum is greater than or equal to a given value.
  assert mini_subarray_sum([1, 4, 45, 6, 0, 19], 51) == 3
  assert mini_subarray_sum([1, 10, 5, 2, 7], 9) == 1
  assert mini_subarray_sum([1, 11, 100, 1, 0, 200, 3, 2, 1, 250], 280) == 4
output: def mini_subarray_sum(arr, target):
      n = len(arr)
      min_length = float('inf')
      current_sum = 0
      start = 0
      
      for end in range(n):
          current_sum += arr[end]
          while current_sum >= target:
              min_length = min(min_length, end - start + 1)
              current_sum -= arr[start]
              start += 1
              
      return min_length if min_length != float('inf') else 0