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992. Subarrays with K Different Integers

Difficulty Topics

Description

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

Solution

subarrays-with-k-different-integers.py
class Solution:
    def subarraysWithKDistinct(self, nums: List[int], k: int) -> int:
        n = len(nums)
        left = prefix = res = distinct = 0
        count = Counter()

        for right, x in enumerate(nums):
            if count[x] == 0:
                distinct += 1

            count[x] += 1

            if distinct > k:
                count[nums[left]] -= 1
                left += 1
                prefix = 0
                distinct -= 1

            while count[nums[left]] > 1:
                count[nums[left]] -= 1
                prefix += 1
                left += 1

            if distinct == k:
                res += prefix + 1

        return res