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Java-based LeetCode algorithm problem solutions, regularly updated

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package g0901_1000.s0992_subarrays_with_k_different_integers;

// #Hard #Array #Hash_Table #Counting #Sliding_Window
// #2022_03_31_Time_4_ms_(99.36%)_Space_46.2_MB_(86.91%)

/**
 * 992 - Subarrays with K Different Integers\.
 *
 * Hard
 *
 * 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`
**/
public 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;
    }
}