g2901_3000.s2916_subarrays_distinct_element_sum_of_squares_ii.Solution

public class Solution extends Object

2916 - Subarrays Distinct Element Sum of Squares II.

Hard

You are given a 0-indexed integer array nums.

The distinct count of a subarray of nums is defined as:

Let nums[i..j] be a subarray of nums consisting of all the indices from i to j such that 0 <= i <= j < nums.length. Then the number of distinct values in nums[i..j] is called the distinct count of nums[i..j].

Return the sum of the squares of distinct counts of all subarrays of nums.

Since the answer may be very large, return it modulo 10⁹ + 7.

A subarray is a contiguous non-empty sequence of elements within an array.

Example 1:

Input: nums = [1,2,1]

Output: 15

Explanation: Six possible subarrays are:

[1]: 1 distinct value

[2]: 1 distinct value

[1]: 1 distinct value

[1,2]: 2 distinct values

[2,1]: 2 distinct values

[1,2,1]: 2 distinct values

The sum of the squares of the distinct counts in all subarrays is equal to 1² + 1² + 1² + 2² + 2² + 2² = 15.

Example 2:

Input: nums = [2,2]

Output: 3

Explanation: Three possible subarrays are:

[2]: 1 distinct value

[2,2]: 1 distinct value

The sum of the squares of the distinct counts in all subarrays is equal to 1² + 1² + 1² = 3.

Constraints:

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