Is Subarrays Distinct Element Sum of Squares I easy or hard?

LeetCode classifies this problem as Easy. The main idea is straightforward: iterate over all subarrays and track distinct elements. The optimization with a hash map reduces redundant work and is commonly expected in interviews.

Subarrays Distinct Element Sum of Squares I Python/Java solution

The typical implementation uses nested loops and a dictionary or hash map. For each starting index, create a frequency map and extend the subarray while updating counts and the number of distinct elements. The square of the distinct count is added to the result at every step. The same logic translates directly across Python, Java, C++, and other languages.

How to solve Subarrays Distinct Element Sum of Squares I in O(n)?

An O(n) solution is not possible because the number of subarrays in an array of length n is n(n+1)/2. Each subarray contributes to the final sum, so at least O(n^2) work is required to evaluate them. The optimal approach therefore maintains distinct counts incrementally and achieves O(n^2) time with a hash map.

What is the best approach for Subarrays Distinct Element Sum of Squares I?

The most practical solution uses an incremental hash map while expanding each subarray. Fix a starting index, extend the right boundary, and maintain element frequencies in a hash table. The number of distinct elements can be updated in O(1), so each extension contributes distinct_count^2 to the total. This reduces the complexity to O(n^2) time and O(n) space.

Is Subarrays Distinct Element Sum of Squares I asked at Google/Amazon/Meta?

Problems involving subarrays, distinct element counting, and hash table frequency tracking are common in interviews at companies like Amazon, Google, and Meta. This exact problem may appear in online assessments or practice sets because it tests understanding of arrays, hash maps, and incremental window expansion.

What data structure is used in Subarrays Distinct Element Sum of Squares I?

A hash table (or dictionary/map) is used to store the frequency of elements in the current subarray. The map allows constant-time updates when extending the subarray and quickly determines whether an element increases the distinct count.

What is the time complexity of Subarrays Distinct Element Sum of Squares I?

The optimized solution runs in O(n^2) time because every subarray start index expands through the remaining elements once. Distinct counts are updated using a hash table in constant time. Space complexity is O(n) for the frequency map that tracks element counts.

Description Hints 1 Solution Video 10:50

2913. Subarrays Distinct Element Sum of Squares I

Easy87.8% acceptance1 company

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.

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 = [1,1]
Output: 3
Explanation: Three possible subarrays are:
[1]: 1 distinct value
[1]: 1 distinct value
[1,1]: 1 distinct value
The sum of the squares of the distinct counts in all subarrays is equal to 1² + 1² + 1² = 3.

Constraints:

1 <= nums.length <= 100
1 <= nums[i] <= 100

Asked at 1 company

Google

Topics

Array Hash Table

Hints open one at a time

Hint 1

Use a set/heap to keep track of distinct element counts.

10:50

Still stuck?Read 3 approaches, or watch a walkthrough.

Open solution

LanguageLoading editor…

1class Solution:
2    def sumCounts(self, nums: List[int]) -> int:
3        

Starter codePython 3Spaces: 4

Examples

Case 1Case 2

Input

[1,2,1]

Input

[1,1]

Your code is saved on this device.Solution