How do you solve Sum of Values at Indices With K Set Bits on LeetCode?

Sum of Values at Indices With K Set Bits (LeetCode #2859) can be solved using Brute Force or Optimal Solution. The optimal approach is Optimal Solution with O(n) time complexity and O(n) space complexity. Key insight: Understanding binary representation is crucial for bit manipulation problems.

What is the brute force solution for Sum of Values at Indices With K Set Bits?

The brute force approach for Sum of Values at Indices With K Set Bits is Brute Force, with O(n log n) time complexity and O(1) space complexity. The brute-force approach involves checking each index of the array to see how many set bits it has in its binary representation. If the count matches k, we add the corresponding value from the nums array to our sum. The optimal Optimal Solution approach improves this to O(n).

What algorithm or data structure is used to solve Sum of Values at Indices With K Set Bits?

Sum of Values at Indices With K Set Bits uses the following concepts: Array, Bit Manipulation. The recommended patterns to study are: Hash Map, Array.

What are the interview tips for Sum of Values at Indices With K Set Bits?

Explain your thought process clearly while coding. Consider edge cases and constraints before jumping into coding. Practice bit manipulation problems to become more comfortable with binary operations.

What are common mistakes when solving Sum of Values at Indices With K Set Bits?

Not counting set bits correctly, especially when using bitwise operations. Overlooking edge cases, such as when k is 0.

#2859

Sum of Values at Indices With K Set Bits

Easy

ArrayBit ManipulationHash MapArray

LeetCode ↗

Approaches

Brute ForceOptimal

Complexity Comparison

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

💡

Intuition

Time O(n)Space O(n)

The optimal solution involves precomputing the number of set bits for all indices up to the length of the nums array. This allows us to quickly check if an index has k set bits without recalculating each time.

⚙️

Algorithm

5 steps

1Step 1: Create an array to store the count of set bits for each index.
2Step 2: Loop through each index and calculate the number of set bits using a helper function.
3Step 3: Initialize a variable sum to 0.
4Step 4: Loop through the nums array and sum the values where the count of set bits equals k.
5Step 5: Return the sum.

solution.py7 lines

1# Full working Python code
2
3def sum_of_set_bits(nums, k):
4    def count_set_bits(n):
5        return bin(n).count('1')
6    set_bits_count = [count_set_bits(i) for i in range(len(nums))]
7    return sum(nums[i] for i in range(len(nums)) if set_bits_count[i] == k)

ℹ

Complexity note: The time complexity is O(n) because we compute the set bits count for each index once and then iterate through the nums array. The space complexity is O(n) due to the additional array used to store the set bits count.

1Understanding binary representation is crucial for bit manipulation problems.
2Precomputing values can significantly reduce time complexity.

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