Fix bug in hint and add explanations

[jericahuang]

Resulting function that passes all tests:

def kth_missing_positive_number(numbers, k):
  if k < numbers[0]:
    return k
  index = 0
  k -= numbers[0]-1
  while index < len(numbers) - 1:
    current_missing = numbers[index + 1] - numbers[index] - 1
    if k <= current_missing:
      return numbers[index] + k
    k = k - current_missing
    index += 1
  return numbers[-1]+k

[kelsey-steven-ada]

Thanks for updating this!

[anselrognlie]

Looks good. I just have a couple suggestions that to me helps the clarity.

[anselrognlie]

Suggest calling out where the 1 is coming from.

Suggested change

	* `k` will be decremented to represent the number of remaining missing nums. This line accounts for missing nums before `arr[0]`.
	* `k` will be decremented to represent the number of remaining missing nums. This line accounts for missing nums before `arr[0]`, which we expect to start from 1, the smallest positive integer.

[anselrognlie]

Suggest accounting for where the 1 is coming from.

Suggested change

	* `current_missing` represents how many missing numbers between `arr[index + 1]` and `arr[index]`
	* `current_missing` represents how many missing numbers there are between `arr[index + 1]` and `arr[index]`, which should differ by only 1 if there are no missing numbers.

[anselrognlie]

We mention that k gets decremented above, but I think noting why again here is helpful.

Suggested change

	* `k = k - current_missing`
	* `k = k - current_missing`
	* Reduce the number of missing numbers we are looking for by the number of missing numbers we just found.