992

class Solution:
    def subarraysWithKDistinct(self, A: List[int], K: int) -> int:

        def at_most_k_distinct(nums, k):
            l = r = res = 0
            memo = defaultdict(int)

            while r < len(nums):
                memo[nums[r]] += 1
                if memo[nums[r]] == 1:
                    k -= 1
                r += 1
                while k < 0:
                    memo[nums[l]] -= 1
                    if memo[nums[l]] == 0:
                        k += 1
                    l += 1

                res += r - l

            return res

        return at_most_k_distinct(A, K) - at_most_k_distinct(A, K - 1)