2025-11-05
3321. Find X-Sum of All K-Long Subarrays II

Topic: Array, Hash Table, Sliding Window, Heap (Priority Queue)
Difficulty: Hard

Problem:
You are given an array nums of n integers and two integers k and x.

The x-sum of an array is calculated by the following procedure:

• Count the occurrences of all elements in the array.
• Keep only the occurrences of the top x most frequent elements. If two elements have the same number of occurrences, the element with the bigger value is considered more frequent.
• Calculate the sum of the resulting array.

Note that if an array has less than x distinct elements, its x-sum is the sum of the array.

Return an integer array answer of length n - k + 1 where answer[i] is the x-sum of the subarray nums[i..i + k - 1].

Example 1:

Input: nums = 1,1,2,2,3,4,2,3, k = 6, x = 2

Output: 6,10,12

Explanation:

• For subarray [1, 1, 2, 2, 3, 4], only elements 1 and 2 will be kept in the resulting array. Hence, answer[0] = 1 + 1 + 2 + 2.
• For subarray [1, 2, 2, 3, 4, 2], only elements 2 and 4 will be kept in the resulting array. Hence, answer[1] = 2 + 2 + 2 + 4. Note that 4 is kept in the array since it is bigger than 3 and 1 which occur the same number of times.
• For subarray [2, 2, 3, 4, 2, 3], only elements 2 and 3 are kept in the resulting array. Hence, answer[2] = 2 + 2 + 2 + 3 + 3.

Example 2:

Input: nums = 3,8,7,8,7,5, k = 2, x = 2

Output: 11,15,15,15,12

Explanation:

Since k == x, answer[i] is equal to the sum of the subarray nums[i..i + k - 1].

Constraints:

• nums.length == n
• 1 <= n <= 10^5
• 1 <= nums[i] <= 10^9
• 1 <= x <= k <= nums.length