992. Subarrays with K Different Integers

Problem

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 * 10^4

• 1 <= nums[i], k <= nums.length

Solution

class Solution {
    public int subarraysWithKDistinct(int[] nums, int k) {
        int res = 0;
        int prefix = 0;
        int[] cnt = new int[nums.length + 1];
        int i = 0;
        int j = 0;
        int uniqueCount = 0;
        while (i < nums.length) {
            if (cnt[nums[i]]++ == 0) {
                uniqueCount++;
            }
            if (uniqueCount > k) {
                --cnt[nums[j++]];
                prefix = 0;
                uniqueCount--;
            }
            while (cnt[nums[j]] > 1) {
                ++prefix;
                --cnt[nums[j++]];
            }
            if (uniqueCount == k) {
                res += prefix + 1;
            }
            i++;
        }
        return res;
    }
}

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(n).