992 Subarrays with K Different Integers

🔀 Pick One

Given an integer array nums and an integer k, return the number of good subarrays of nums.

A good array is an array where the number of different integers in that array is exactly k.

  • For example, [1,2,3,1,2] has 3 different integers: 1, 2, and 3. A subarray is a contiguous part of an array.

Example 1:

Input: nums = [1,2,1,2,3], k = 2
Output: 7
Explanation: Subarrays formed with exactly 2 different integers:
[1,2], [2,1], [1,2], [2,3], [1,2,1], [2,1,2], [1,2,1,2]

Example 2:

Input: nums = [1,2,1,3,4], k = 3
Output: 3
Explanation: Subarrays formed with exactly 3 different integers:
[1,2,1,3], [2,1,3], [1,3,4].

Constraints:

  • 1 <= nums.length <= 2 * 104
  • 1 <= nums[i], k <= nums.length
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class Solution:
    def subarraysWithKDistinct(self, nums: List[int], k: int) -> int:
        n = len(nums)
        
        def at_most_k(k):
            count = collections.defaultdict(int)
            res, i = 0, 0
            for j in range(n):
                # move window right
                if count[nums[j]] == 0:
                    k -= 1
                count[nums[j]] += 1
                while k < 0:
                    # move window left
                    count[nums[i]] -= 1
                    if count[nums[i]] == 0:
                        k += 1
                    i += 1
                # add windows size (with at most k distinct)
                res += j - i + 1
            return res

        return at_most_k(k) - at_most_k(k-1)