LeetCode Problem Number: 2859

Problem Description

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.

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.

Solution Code

class Solution {
public:

    int getSetBits(int n){
        int count = 0;
        while(n > 0){
            if(n & 1) count++;
            n = n >> 1;
        }
        return count;
    }

    int sumIndicesWithKSetBits(vector& nums, int k) {
        int sums = 0;
        for(int i = 0 ; i < nums.size() ; i++){
            if(getSetBits(i) == k){
                sums+=nums[i];
            }
        }
        return sums;      
    }
};
                    

Solution Explanation

The problem involves calculating the sum of XOR totals for every subset of a given array. The solution follows these steps:

• Counting Set Bits: A helper function getSetBits counts the number of 1's in the binary representation of an integer.
• Iterating Through Indices: For each index in the array, if the number of set bits matches k, its corresponding value is added to the sum.
• Time Complexity: This approach runs in O(n log m) time, where n is the number of elements in the array and m is the maximum value of indices, due to bitwise operations.