Sum of Values at Indices With K Set Bits

export function sumIndicesWithKSetBits(nums: number[], k: number): number {
  function countBit(num: number) {
    let count = 0;
    while (0 < num) {
      count += num & 1;
      num = num >> 1;
    }
    return count;
  }
 
  return nums.reduce((acc, num, i) => (countBit(i) === k ? acc + num : acc), 0);
}