Leetcode 2354. Number of Excellent Pairs

Count ordered pairs (a, b) from values in nums whose bit-counts satisfy popcount(a)+popcount(b) >= k. Key insight: popcount(a|b)+popcount(a&b)=popcount(a)+popcount(b), so deduplicate values, tally frequencies of popcounts (0–30), and count pairs of counts whose sum ≥ k.