Solution 8: Minimal Length Subarray

Given an array of positive integers and a positive integer target value, return the minimal length of a subarray which has a sum greater than or equal to target. If there is no such subarray in the array, return 0.

def min_sub_array_len(target, nums)
  sub_array_length = 0
  start_index = 0
  end_index = 0

  loop do
    sub_array_sum = get_sum(nums, start_index, end_index)
    if (sub_array_sum < target)
      end_index += 1
    elsif (sub_array_sum > target)
      start_index += 1
    else
      this_array_length = (end_index - start_index) + 1
      sub_array_length = if sub_array_length == 0
      this_array_length
    else
      sub_array_length < this_array_length ? sub_array_length : this_array_length
    end
      end_index += 1
    end

    if (end_index >= nums.length)
      break
    end
  end

  sub_array_length
end

def get_sum(array, start_index, end_index)
  sum = 0
  for number in array[start_index..end_index]
    sum += number
  end
  sum
end