Bits — Total Hamming Distance

The Hamming distance of two integers is the number of bit positions where they differ.
solve(nums) — nums holds non-negative integers < 2^31. Return the **sum of the Hamming
distances over all pairs** (i, j) with i < j.

Comparing every pair is O(n²). Count per bit instead: if ones of the n numbers
have a given bit set, then ones × (n - ones) pairs differ on that bit. Sum that over
the 31 bit positions for an O(31 · n) solution.

Examples

solve([4,14,2])   → 6
solve([4,14,4])   → 4
solve([1,2,3])    → 4