How do you solve Sum of Squares of Special Elements on LeetCode?

Sum of Squares of Special Elements (LeetCode #2778) can be solved using Brute Force or Optimal Solution. The optimal approach is Optimal Solution with O(n) time complexity and O(1) space complexity. Key insight: Understanding how to identify special indices is crucial for solving this problem efficiently.

What is the brute force solution for Sum of Squares of Special Elements ?

The brute force approach for Sum of Squares of Special Elements is Brute Force, with O(n) time complexity and O(1) space complexity. We will check each index of the array to see if it is a special index (i.e., if it divides the length of the array). If it is special, we will add the square of the element at that index to our total sum. The optimal Optimal Solution approach improves this to O(n).

What algorithm or data structure is used to solve Sum of Squares of Special Elements ?

Sum of Squares of Special Elements uses the following concepts: Array, Enumeration. The recommended patterns to study are: Enumeration, Array.

What are the interview tips for Sum of Squares of Special Elements ?

Always clarify the indexing system (1-based vs. 0-based) with the interviewer. Think aloud while solving; it helps the interviewer understand your thought process. Consider edge cases, such as the smallest and largest possible inputs.

What are common mistakes when solving Sum of Squares of Special Elements ?

Forgetting to adjust the index when accessing elements in a 0-based array. Not properly checking the condition for special indices.

#2778

Sum of Squares of Special Elements

Easy

ArrayEnumerationEnumerationArray

LeetCode ↗

Approaches

Brute ForceOptimal

Complexity Comparison

	Brute Force	Optimal Solution★
Time	O(n)	O(n)
Space	O(1)	O(1)

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Intuition

Time O(n)Space O(1)

We can directly compute the sum of squares of the special elements by iterating through the indices that divide n, which reduces unnecessary checks.

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Algorithm

4 steps

1Step 1: Initialize a variable to hold the sum of squares.
2Step 2: Loop through each index from 1 to n (inclusive).
3Step 3: For each index, if it divides n, add the square of nums[i-1] to the sum.
4Step 4: Return the total sum.

solution.py9 lines

1# Full working Python code
2
3def sum_of_squares(nums):
4    n = len(nums)
5    total_sum = 0
6    for i in range(1, n + 1):
7        if n % i == 0:
8            total_sum += nums[i - 1] ** 2
9    return total_sum

ℹ

Complexity note: The optimal solution also runs in O(n) time, as we only loop through the array once, and uses O(1) space since we are not using any additional data structures.

1Understanding how to identify special indices is crucial for solving this problem efficiently.
2Recognizing that we only need to check indices that divide n helps streamline the solution.

Solutions and explanations are original Tejav content. Problem titles © LeetCode — use the LeetCode button above for the full problem statement.