Introduction

In this blog post, we will explore how to solve the LeetCode problem "2859" using AI. LeetCode is a popular platform for preparing for coding interviews, and with the help of AI tools like Chatmagic, we can generate solutions quickly and efficiently - helping you pass the interviews and get the job offer without having to study for months.

Problem Statement

You are given a 0-indexed integer array nums and an integer k. Return an integer that denotes the sum of elements in nums whose corresponding indices have exactly k set bits in their binary representation. The set bits in an integer are the 1's present when it is written in binary. For example, the binary representation of 21 is 10101, which has 3 set bits. Example 1: Input: nums = [5,10,1,5,2], k = 1 Output: 13 Explanation: The binary representation of the indices are: 0 = 0002 1 = 0012 2 = 0102 3 = 0112 4 = 1002 Indices 1, 2, and 4 have k = 1 set bits in their binary representation. Hence, the answer is nums[1] + nums[2] + nums[4] = 13. Example 2: Input: nums = [4,3,2,1], k = 2 Output: 1 Explanation: The binary representation of the indices are: 0 = 002 1 = 012 2 = 102 3 = 112 Only index 3 has k = 2 set bits in its binary representation. Hence, the answer is nums[3] = 1. Constraints: 1 <= nums.length <= 1000 1 <= nums[i] <= 105 0 <= k <= 10

Explanation

• Iterate through the array: Loop through the nums array, using the index as the key to check the number of set bits.
  • Count set bits: For each index, efficiently determine the number of set bits in its binary representation.
  • Conditional Summation: If the set bit count matches k, add the corresponding element in nums to the running sum.

• Runtime Complexity: O(N), where N is the length of the nums array. Storage Complexity: O(1)

Code

    def sum_indices_with_k_set_bits(nums, k):
    """
    Calculates the sum of elements in nums whose corresponding indices have exactly k set bits.

    Args:
        nums: A 0-indexed integer array.
        k: An integer representing the target number of set bits.

    Returns:
        An integer denoting the sum of elements in nums whose corresponding indices have exactly k set bits.
    """

    total_sum = 0
    for i in range(len(nums)):
        set_bits = 0
        index = i
        while index > 0:
            index &= (index - 1)  # Efficiently clear the least significant set bit
            set_bits += 1

        if set_bits == k:
            total_sum += nums[i]

    return total_sum